I had the same problem with my Fw 190 D9 disappearing underneath the surface. Even plunging before take-off. I found that the problem was caused by the WW2 AIRCRAFT MODS, but to solve the problem, you don't have to delete the complete files, just deleting the FW190A4 and A5 folders solved the problem.
So I'm quite sure the problem is caused by common files used by a mod. (e.g. the A-4 causing the problem for planes using the same files)
Hope this can help some people.