Ad inserter doesn’t show media.net ads

I logged a case about the same issue before a month with no showing media.net ads. The problem disappeared (not sure how). Now it appeared again.
I have installed media.net with ad inserter before 2 months and till now everything was working.
As of a couple of days, the ads don’t show.
I re-installed the plugin, stopped the plugins one by one, checked the debugging mode but I can’t understand where is the problem.
The blocks with the code are inserted but the code doesn’t display anything.
Media.net indicates that the codes are detected.
I haven’t changed anything in the initial configuration of the setup.
What can be the problem?

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