I’m surprised you had no trouble importing the XML from Resolve into FCPX since by default Resolve generates an FCPXML 1.3 (which is for FCPX 10.1).
Make sure nothing got screwy in the inspector: transform size set to 0%, or a mask that’s hiding everything.
You can try exporting the XML of this corrupt project from FCPX and then reimport it.
Any reason you haven’t upgraded to FCPX 10.1.1? 10.0.6 is very buggy.
Best,
Jerome
Jerome Raim
Post-Production
JeromeRaim.com