Mike
I have used Opus in all it's variant since version 2. I use it most days, sometimes for 6-8 hours per day. I also run CCleaner several times each week.
This probably isn't what you want to hear, but I have fortunately never come across the problems that you describe.
Often weird and wonderful happenings like this can be traced back to a corrupt registry entry for Opus, in which case it should be solved by an uninstall followed by clean install of Opus. There are several posts that describe in detail how to do this. Try searching for "uninstall" or "registry" or whatever else takes your fancy.
Another cause of some problems can relate to problems with drivers, but from your description, this seems unlikely, although I'm ready to be corrected on this.
Even less likely, but still possible can be hardware problems. What is your hardware + OS specs? It helps us to identify problems if you include these specs in your signature so they always appear in your posts.
I recall having intermittent and unusual problems some months back which were finally traced back to problems in the power supply unit. The lack of consistent power apparently caused issues with the stability of some hardware elements, which passed it on to the software. I didn't understand the whys, but swappping in another PSU solved that problem.
More recently I encountered another lot of instability. This was identified as a faulty memory address. Removing the faulty memory stick solved that issue. Reminds me that I need to revise my RAM to 2GB in my signature
I'm not saying that the problem doesn't lie with Opus, but I find it an improbably candidate. I cannot recall seeing this combination of reports posted before, and I'm pretty sure that if it was a problem related to Opus 5.5, someone would have encountered it by now.
Hope you resolve the problem soon.