Hi,
the same problem here.
In my case only at the first call of an modal VI from floating VI the modal VI was not before the floating VI frontpanel.
Check: Push the floating VI to a side, so you can reach the modal VI, when it open (normally in the center of the screen). Close it, and open it again. In my case it was now in front of the floating VI.
So I call a empty modal VI at start, which closes directly after start and the afterwards calls of other modal VIs work fine.
It is a shame, but it works in my case.