When I swim / crawl, my view is stuck at the normal height, here's my modlist;
https://pastebin.com/EtHynRbv

Problem was Galacticraft, and from the other issue related to it, it doesnt sound like it'll get fixed

Do you have Player API installed as well? If I recall correctly I made it work with GC when that is present.

just remove chunks of mods until you see issue is gone, then define what mod causes the issue

I did not, I will test that.