Guild Wars 2

since 2 days it is no longer possible to split stack by holding alt and dragging to a new inv spot.

Works for me.

Is your Alt key not broken, by chance?

Works for me, too – if you’re on a Mac or in Linux using a wine derivative, click and hold FIRST, then press alt – doing it the other way around gets funky occasionally (no rhyme or reason).

Also works for me.

I haven’t had any issues with it (today or otherwise), either.

If you have eliminated the possibility that your ALT key is malfunctioning, you might try a -repair of the client.

https://help.guildwars2.com/entries/28148006-Repairing-the-Game-Client

Good luck.