Problem Details:

when you use short links like [[AR]] it normally leads you to https://osu-ppy-sh.tvgratuite.org/wiki/AR
(you will have to scroll to the content instead of getting automatically moved to it)

like you can see, it ignored/removed the #... for whatever reason

Well, this used to work properly iirc, yes. Confirming.

So it wasn't just my imagination...

Are you talking about when you make these links inside wiki articles, or from the osu! game client itself?

e.g. if I type [[AR]] or https://osu-ppy-sh.tvgratuite.org/wiki/Song_Setup

also if I type [[Song_Setup#Approch_Rate]] and open it it will just open https://osu-ppy-sh.tvgratuite.org/wiki/Song_Setup

PS: it doesn't look like a client bug 'cause when I write the URL (https://osu-ppy-sh.tvgratuite.org/wiki/Song_Setup#Approch_Rate) instead