Same thing happening here with my Diamond 7970, although GPUVRM only quits reporting when my monitors sleep.
I have two power plans set up for this machine, "Always On" and "Monitors Off" (turns off displays after 1 minute). With the power setting "Always On", there's no problem - not even intermittent. With the power setting "Monitors Off", GPUVRM temp no longer shows after waking monitors. GPUVRM then shows after a restart of AIDA64.
atismbusdump1.txt = running normally
atismbusdump2.txt = after GPUVRM quits reporting
Let me know if I can provide any further info...Thanks!
atismbusdump1.txt
atismbusdump2.txt