Your ad units are possibly misconfigured.
Step 1: Audit the div ID’s to make sure it matches.
There are 3 places where your div ID should be found or configured. Audit the following:
Ad unit code
PubGuru header bidding configuration (if running Header Bidding)
Within <head> </head>
Within <body> </body> (should match the div ID’s in the Header)
Audit your ad units in Ad Manager. Status should say ‘Active’
Step 2: Re-check your PubGuru header bidding configuration to make sure you have the correct Network ID configured for each ad unit