AbuseFilter diffs involving at least one old change to a filter, such as https://www.mediawiki.org/wiki/Special:AbuseFilter/history/1/diff/prev/2, are failing to load with a TypeError:
Error message
[X-fQxgpAMMMAAjeGGFEAAACA] 2021-01-08 03:25:58: Fatal exception of type "TypeError"