That sounds like the blocks got orphaned (as explained previously). Essentially that means that your wallet thought it had found those blocks while the network did not agree. This is something that most commonly happens when your wallet is not in sync with the network, causing your local blockchain to fork (and then by the time you start syncing with the network correctly again, those blocks get orphaned). This is not specific to SAT, this would've happened with any other coin too if you end up on your own fork.

Also - you mentioned that you had mined about 400k SAT in a week. This translates to a hashrate which would make more sense in a pool, rather than mining directly to your wallet. As such, I would recommend to look into that.