You are possibly running an old version of PubGuru header bidding. Try upgrading and re-run PubGuru Ad Inspector (PGAI).
Step 1: Open the relevant PubGuru header bidding configuration
Step 2: Upgrade your header bidding version
Step 3: Save & Publish the config.
Step 4: Re-run PubGuru Ad Inspector (PGAI)
Step 5: Contact email@example.com if the error continues to persist.