The following requests in some wikis (eg. Wikisource, Wikinews, Commons):
https://pl.wikisource.org/wiki/Specjalna:Aktywni_u%C5%BCytkownicy?username=&excludegroups%5B%5D=bot&wpFormIdentifier=specialactiveusers https://en.wikisource.org/wiki/Special:ActiveUsers?username=&excludegroups%5B%5D=bot&wpFormIdentifier=specialactiveusers
gives a database error:
A database query error has occurred. This may indicate a bug in the software. [WJLSBgpAEK8AAHTExmkAAAIB] 2017-02-02 06:30:30: Fatal exception of type "DBQueryError"
Worked yesterday.
No error eg. on enwiki