I was looking at DiscussionTools error logging for some other reason, and I noticed that there's a large number of 'maxchars' errors, starting on 2021-11-05 (87 in total).
This probably comes from rEDTO6022982eb93c: Generate form tokens in the client to prevent double posting, are we generating client-side tokens larger than the server-side code allows?
Query for https://superset.wikimedia.org/superset/sqllab/:
select year, month, day, count_if(event.save_failure_message='maxchars') as count from editattemptstep where event.integration='discussiontools' and event.action='saveFailure' and year=2021 and month>=10 group by year, month, day order by year, month, day