This was years ago for me, but as bad as it is losing the amount earned, it was just the lack of response when trying to understand why you were terminated. I had no idea why I was banned. I didn't employ any shady tricks. The only thing I noticed in the few weeks prior to the account banned was a higher CTR.

I actually emailed Adsense support at that time to let them know that it was out of the ordinary for my site.

Additionally, I also had an account on the CPA affiliate side of things with the same account that was banned because it was tied with the Adsense email account.