Hi,
just a couple of possible tests: in this post on RBF I tried to axplain some troubles when using RBFMeshMotionSolver with preCICE. Another thing that you could try is to convert the flexible DAM Break case in the solids4foam repository to make it work with RBFMeshMotions solver. Everything you should need is inside s4f (no preCICE, no other software…), if you manage to make it work there, maybe you can extend it to your case. I will be able to make some test on my side next week…
Claudio