No worries, I appreciate your efforts all the same ^^
I’ve just been trying a few things to fix the issue myself, and something I did seems to have done it - the corruption has completely stopped
I’ve also updated to 1.11, restarted browser and line 290 (the line that always got corrupted) was exactly as it should be. So hopefully that’s that. 
For my own reference and in case it helps anyone else, here’s what I did:
I reinstalled TamperMonkey, updated my language packs (Japanese and English UK), cleared my browser cache and (after exporting my scripts) I did a factory reset on TamperMonkey
I’m guessing it was the TamperMonkey reinstall or reset that did it, but I try to be thorough



Maybe the green from the review forecast? 


Until now I had used