sounds like a setup problem
have you already confirmed the software is working by running a cantilever beam or similar that you know the answer for?
if this works, the software is working fine and it is either a problem specific to your assembly or a setup problem
then you can take your assembly, remove complexities until it is down to a problem that you can easily find the answer, if it comes back ok, then it is a setup problem that you have to isolate.
my guess would be that you have a large displacement warning that you're ignoring or soft springs/inertial releif enabled.