I'm guessing we need to update ArticleFeedbackv5 since I was able to just properly mark feedback on social-tools.wmflabs.org which is using the latest version - http://social-tools.wmflabs.org/w/index.php?title=Special:ArticleFeedbackv5/ArticleFeedbackv5&ref=cta#05671d43315bc47a0eab00163e69db65
I don't happen to know whether or not the master version is compatible with 1.26.2, however.
relevant IRC conversation from earlier today (which mentions T152737: Database error and/or MediaWiki exception occurs upon trying to edit on Brickipedia):
[11:57:18] <+ashley> I can see the problem (there should be the option to do something about the feedback, but there isn't), but there's nothing exciting in the error logs or anything -- the DB error log is basically full of OOM errors, no "real" ones [11:58:40] <SamanthaNguyen> that sounds like it's just falling back to T152737 then [11:58:46] <SamanthaNguyen> https://phabricator.wikimedia.org/T152737 [11:59:14] <SamanthaNguyen> are you fine with me closing the aftv5 ticket as a duplicate? [12:02:57] <+georgebarnick> Well it's certainly the same issue that causes it but the fact that one database error that I incurred yesterday prevents article feedback from ever being usable again is kinda a different issue [12:05:31] <SamanthaNguyen> OK, I'll keep them separate