When recording different takes I had some audio recordings. where the waveform region showed up as empty and did not play back. (See below)
After restarting Cubasis the waveform the displayed properly and the recording played back as recorded.
If this is of any help, I think this was a duplicated (cloned) track, Audio Units: Fabfilter Pro Q3, Pro C 2, Busfri and Waves: Audio Track. When I tried to replicate the issue it didnt happen again. Sample rate 48 and 24bit. Buffer 5.8, multicore enabled, default safety buffer.