I’m having the same problem here as well.
On top of that, if I “back up” a project, the sampler tracks in the new project still reference the old audio files (despite copying the samples to the new audio folder too). If I trick Cubase to have to look to the new files (by renaming the old project folder and pointing the missing samples to the new audio pool), it will load but any Sampler Tracks using “Solo” mode won’t playback.
I think this has been a problem for at least a year. I really like the Sampler track and I would really like for this to get fixed.