It seems to be an interaction specifically between Sodium 0.5.11 and Paxi 5.0.0. Tested with a clean install of Minecraft with no other mods included and got the same results. Will submit a new issue to the Sodium devs as well.

Between this and #30 as well as some user reports in the discord, it seems the 1.21 version may have issues loading builtin resources in an unexpected order. I'll try to look into it as soon as I can.