The web version doesn't work well with 3D at some point, at least in my experience with Godot Engine but I think it's common to all major game engines. I think in this game jam you are allowed to to upload different builds for the game if you didn't add any feature or bug fix so you can try asking the staff if you're allowed to do so. (Just a word of caution: I'm not accountable for anything if you do something bad without asking them!)
I tried doing what you say already but it didn't help :/ But if you try the solution above I think you might have something working BUT - even better! I know an HTML version is important for easy access but sometimes it's better to scrap it if performances are too poor ^^