Thank you for bringing this question to our attention. I was able to check out the link that you gave and have also looked over a few other things. To get a better idea of what might be happening.
When looking at the link you posted and this link
. It would appear to be that there is an issue within the Admob callback and Unity when dealing with the TMP. It seems that Admob is called on a different thread then Unity is and when that thread is used the callback doesn't always function properly to the TMP. Which seems to cause some of the issues.
From what I can tell it would appear to be getting looked a. And the best recommendation has been to remove any logic out of the callback for the when ad is closed to be in te Unity thread instead. When dealing with anything from TMP.
Mobile Ads SDK Team