Does your system do the things you want it to do?
Does your system blue screen or freeze if you are not running prime?
Running prime just proves that your system can run prime, nothing more. Stable is if your system can do all the things you need your PC to do in 24/7 us e. Now if Prime is your 24/7 use for your PC fair enough. Stable is as stable does mate.
I know people who have systems that are 48 hours prime stable but fail the minute they start to play WOW on line, I kid you not. I have been in this industry for a couple of years, and been a bencher for a while and honestly I do not get this fascination with prime. Not one bit. True I will use Prime to check were an overclock is for a system I am putting together for others but anything more that 1 or 2 hours is just pointless to me.
There are my views and most certainly do not represent the views of most folks. 🙂
Back to your issue, if prime is where you want to be at then run stock and see if stock passes prime after a sleep.
To help us help you - please provide as much information about your system and the problem as possible.