There’s probably already a thread about this, but I’m unsure of the terminology, which makes searching for it difficult.
Let’s say you put the cursor in the middle of a track and split it with Ctrl+I. You can then merge it back together by clicking on the seam. For a long time (i.e., many versions of Audacity), clicking on splits has been very dangerous, and I’ve learned to save beforehand and be very deliberate in how I click on them. No sudden movement, don’t make eye contact, etc. I thought the issue had been resolved in v2, but just the other day I clicked and it thought for a while, gave me the spinning ring, then notified me that Audacity had stopped working. Whenever this happens, I recover the project, click on the same split, and it works fine. …But I’d rather not waste the time recovering (I work with movie length files).
Clicking at split lines usually causes crash problems because there is actually a hidden clip comprising a single audio sample at a point close to the real split line. You cannot see both clips until you zoom in far enough to see all the individual sample dots.
The best suggestion I have is that the next time you experience this crash, please before reopening Audacity: