Understand why some ad units in Google Ad Manager fail to perform well and learn actionable tips to fix and optimize them.

🖋 By Meenakshi – AZAD Architects, Barnala

Why do some ad units underperform in Google Ad Manager?

Even with proper setup and strategy, some ad units in Google Ad Manager (GAM) may generate lower revenue, fewer impressions, or poor engagement. This underperformance can stem from a variety of technical, strategic, or content-related issues that limit ad visibility or competitiveness in auctions. For publishers aiming to maximize their monetization potential, identifying and correcting these issues is crucial. In this blog, we explore the most common reasons why ad units underperform in GAM and how you can turn them into top earners.

Poor Ad Viewability and Placement Issues

How below-the-fold positioning, cluttered layouts, and slow-loading pages reduce ad visibility and engagement.

• Below-the-Fold Positioning

• Ads placed too far down the page are often never seen by users who do not scroll.
  

• Low viewability reduces auction competitiveness and CPMs.
  

• Cluttered or Overloaded Layouts

• Pages with too many ads or a messy design can lead to banner blindness—users ignore them.
  

• Google may reduce bid density on cluttered layouts to protect user experience.
  

• Slow Page Load Speeds

• If ads load after users have scrolled past them, viewability drops drastically.
  

• Poor Core Web Vitals or unoptimized scripts can delay ad rendering.
  

• Ads Competing with High-Engagement Content

• Placing ads near video players, large images, or auto-play elements can distract users from noticing the ad.
  

• Ads need to be visually balanced with content to stand out.
  

• Non-Sticky or Static Placements on Mobile

• Mobile users scroll quickly; non-sticky ads are often missed before loading fully.
  

• Consider anchor or sticky formats to maintain visibility on smaller screens.
  

• Lack of Responsive Design

• If ad units do not adjust well on various devices, they may not render correctly or appear at all.
  

• Use responsive ad units to ensure visibility across all screen sizes.
  

• Overuse of Pop-Ups or Interstitials

• These can interrupt user experience and cause users to bounce, reducing the chance for other ad units to be seen.
  

• Also risks policy violations and revenue penalties.

Weak Demand or Low Competition on Inventory

Why lack of advertiser interest, improper targeting, or missing demand partners can result in lower CPMs and fill rates.

• Lack of Advertiser Demand for Niche Content

• If your site covers a very specific or low-commercial-interest topic, fewer advertisers may bid on it.
  

• This leads to lower CPMs and reduced fill rates.
  

• Improper or Broad Targeting Settings

• Poorly defined or overly broad targeting (e.g., no geographic filters or vague key-values) can cause ads to miss relevant buyers.
  

• Narrow, well-defined targeting attracts higher-paying demand.
  

• Missing or Unlinked Demand Sources

• If AdSense, AdX, or third-party SSPs are not linked or active, you are missing out on demand competition.
  

• Fewer bidders = lower bids.
  

• No Access to Programmatic Deals or Private Marketplaces

• Without preferred deals, programmatic guaranteed, or PMPs, inventory is often sold at open exchange rates.
  

• Direct relationships can significantly increase bid value.
  

• Unattractive or Overused Ad Placements

• If your layout has not been refreshed or your ad unit looks outdated, advertisers may avoid bidding.
  

• Consider refreshing your layout or testing native ad formats.
  

• Time-Based Traffic Variations

• Ad performance may drop during off-peak hours or low-demand seasons (e.g., post-holiday months).
  

• Use dayparting strategies to align delivery with high-demand times.
  

• Limited International Appeal

• Sites focused only on one region may attract fewer global bidders, especially if the market has low average CPMs.
  

• Consider offering content in multiple languages or regions.
  

• Low Historical Ad Performance

• If your inventory has previously had low CTR or viewability, advertisers may avoid it.
  

• Improve performance to regain advertiser trust.
  

Misconfigured Ad Units and Size Mismatches

Explore how incorrect ad sizes, broken tags, or targeting mismatches lead to lower auction participation and errors.

• Incorrect Ad Size Settings

• If the ad size defined in Google Ad Manager does not match the size in your page’s ad slot, ads will not render.
  

• Always ensure size compatibility between ad unit settings and tag implementation.
  

• Outdated or Broken Ad Tags

• Using incomplete, outdated, or incorrectly pasted GPT (Google Publisher Tags) can prevent ads from serving.
  

• Even a minor syntax error can block the entire ad request.
  

• Missing or Incorrect Div IDs

• Each ad unit must have a unique and correctly referenced <div> ID in the HTML.
  

• If the ID does not match the tag or is duplicated, the ad will not appear.
  

• Improper Key-Value Targeting

• If the key-value pairs set in the tag do not align with what is targeted in the line item, ads may be skipped.
  

• Leads to missed bidding opportunities or under-delivery.
  

• Unregistered or Unlinked Ad Units in GAM

• If an ad unit tag is on your site but not defined in your GAM inventory, it will not be eligible for serving.
  

• Always create and map ad units properly inside Google Ad Manager.
  

• Wrong Creative Size for the Targeted Slot

• If the assigned creative does not match the available ad size, it may not render at all.
  

• Use multi-size targeting or responsive creatives for flexibility.
  

• No Backup or Fallback Line Items

• If your line item has limited eligibility or targeting, and no fallback is available, the ad unit may stay blank.
  

• Always set up remnant or default fill campaigns as a backup.
  

• Improper Header Bidding or Tag Conflicts

• Misconfigured header bidding setups or conflicting scripts (e.g., multiple SSPs) can result in delivery issues.
  

• Test ad tags carefully to avoid call clashes and timeouts.

Limited Optimization and Performance Tracking

Understand the impact of not A/B testing, missing performance reports, and skipping routine ad unit analysis.

• No A/B Testing of Ad Layouts or Placements

• Without A/B testing, you will not know which ad sizes, formats, or positions perform best.
  

• Regular testing helps identify high-earning ad placements and eliminate underperformers.
  

• Skipping Regular Performance Reviews

• Many publishers forget to analyze ad unit reports on a weekly or monthly basis.
  

• Ignoring trends in CPM, viewability, or CTR can lead to missed revenue opportunities.
  

• Overreliance on Default Settings

• Using default targeting, pacing, or line item priorities may work for beginners but fails to optimize performance at scale.
  

• Custom settings tailored to your audience and content yield better results.
  

• Not Adjusting to Traffic Changes

• Traffic sources and user behavior change over time—what worked last quarter may not work now.
  

• Lack of adjustment can lead to declining fill rates or lower engagement.
  

• Inadequate Use of GAM’s Reporting Tools

• Failing to use dimensions like device, geography, and ad unit performance means you are missing key optimization data.
  

• Google Ad Manager provides detailed reporting dashboards—use them to fine-tune strategies.
  

• Ignoring Viewability and Engagement Metrics

• If you do not track viewability, CTR, and time-on-site, you cannot identify why users are ignoring certain ad units.
  

• Low engagement can be corrected with placement or format changes.
  

• Lack of Experimentation with Formats

• Not testing new ad formats like sticky ads, native, or video reduces your potential to boost revenue.
  

• GAM supports format diversification for a reason—leverage it.
  

• No Benchmarking or Historical Comparison

• Without comparing current performance to past results, it is hard to spot performance drops or improvements.
  

• Set regular benchmarks and KPIs to guide your optimization efforts.
  

📌 Thank you!

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