Hotbar becomes black when in a match on pvplegacy (play.pvplegacy.net)

not sure how to reproduce this bug, I tried replicating it on a single player world and a server by wearing armor/a kit but couldn't replicate it. The issue is not caused by other mods because I tried it without any other mods and it still happened. It doesn't happen in the lobby but only in a match which might be related to whether wearing armor could be the issue. no resource packs were used.

With mod in a match

Without mod in a match

I've seen this happen before, and will try fixing this soon

In which situations do you have this issue? I'm trying to recreate this, currently seems to only apply in singleplayer