The edit_delta variable is randomly not shown in some abuse filter log details

I noticed this bug a couple of weeks ago at https://de.wikipedia.org/wiki/Spezial:Missbrauchsfilter/155 (and used „new_size - old_size“ as a workaround instead). Having more time to look into this now, I noticed that other abuse filters are affected as well.
It doesn't seem to make a difference wether a filter is logging/warning/disallowing or wether it's a private/public filter.

It's probably easiest for you to look into a public filter, so I recommend taking a look at https://de.wikipedia.org/wiki/Spezial:Missbrauchsfilter/6 or https://de.wikipedia.org/wiki/Spezial:Missbrauchsfilter/202

https://de.wikipedia.org/wiki/Spezial:Missbrauchsfilter-Logbuch/862671 shows the edit_delta variable while https://de.wikipedia.org/wiki/Spezial:Missbrauchsfilter-Logbuch/861732 doesn't.

https://de.wikipedia.org/wiki/Spezial:Missbrauchsfilter-Logbuch/854279 shows the edit_delta variable while https://de.wikipedia.org/wiki/Spezial:Missbrauchsfilter-Logbuch/859395 doesn't.

Looking at some random abuse filters of other projects, I didn't notice anything wrong at https://meta.wikimedia.org/wiki/Special:AbuseFilter/301, https://meta.wikimedia.org/wiki/Special:AbuseFilter/291 and https://en.wikipedia.org/wiki/Special:AbuseFilter/11 but noticed the same bug at https://test2.wikipedia.org/wiki/Special:AbuseFilter/23 – https://test2.wikipedia.org/wiki/Special:AbuseLog/3696 shows the edit_delta variable while https://test2.wikipedia.org/wiki/Special:AbuseLog/3701 doesn't.