Now when I drag an audio file into the sampler track the waveform just disappears!
You can still play it back but the is blank with the ‘Drop audio file here’ dialog showing.
If mainly happens with projects which have more than 1 audio track , so could be with a few 
And if you click on any other track or zone item, and back to sampler / sampler track, waveform shows up (in my case at least)
Yeah but I don’t know anyone that uses only 1 audio track
You might want to add to that bug report that you can reproduce it, dogeatdogg.
I already did.
It’s a bug. Hopefully it won’t take months before an update.
I mean, you should add reproduction steps or it is not a valid report. Check the sticky.
I did. It’s been acknowledged.
No steps necessary other than dropping an audio file and not seeing a waveform.