Hmm...
So we have a situation where several people experience the same problem, and others (perhaps unfortunately including the developers) can't reproduce it at all. So what do we do?
It's all very well saying it's trackable on your machine, and I'm perfectly happy to believe that, but I think you're either going to have to give us a bit more, otherwise we won't be able to distinguish what's different about the machines that exhibit this, and those that don't. Yes I know the developers should be doing this really, but I think we can probably do a bit more here first, even if it's only to remove a few possibilities.
One of the things I noticed about your original screen-grab was that it doesn't only say that the disk might be full - it also says that the destination might not be available, and I believe that may be significant because of the way any save (and write) works in Waveform view. They are based on saves from a temp file, so can we have a look at that? How do you have the primary temp file set up on your machine? It would be an interesting experiment, if you have an external SSD available, to relocate your temp file to a folder on that and see if anything alters about this behaviour.
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