In mods with custom fluids, the player will pass right through custom fluids as if they were air.
For example, see this issue here: https://github.com/TeamPneumatic/pnc-repressurized/issues/663
I've been led to believe that it's because support hasn't been fully added in Forge, but it's been hard to find information about it. If it's true that it hasn't worked since 1.12 as mentioned in that issue, is a fix on the radar or coming anytime soon?
Thanks