That's probably because T-Rex is relatively new and only got introduced to most profit switching software recently, personally only seeing this issue appeared (on 1 card only in a 3 card rig) no more than 5 hours ago.
To elaborate on the situation, it probably is due to Nvidia driver crash/reset, check your event log for possible errors from driver such as nvlddmkm ... etc. If you have these driver errors, tone down your OC would be the very first important step to try.
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@Patrike & T-Rex dev (if you are still following the thread)
So what happens is that unlike some driver crashes, where the computer needed to be rebooted, or manually disable/enable individual GPU through device manager in order for Afterburner to recognise the card, the situation with T-Rex that I have seen today (probably related to @trucobit's anyway) is that the driver recovered from errors:
\Device\UVMLiteProcess469
Graphics Exception: SKEDCHECK05_LOCAL_MEMORY_TOTAL_SIZE failed
\Device\UVMLiteProcess469
Graphics Exception: ESR 0x407020=0x1000 0x407028=0x0 0x40702c=0x900c064 0x407030=0x0
and Afterburner was able to pickup the card readings completely fine, so does T-Rex miner and AM having no trouble initialising and running mining sessions with all GPUs functional. Bear in mind that T-Rex's current implementation does not include GPU monitoring, so the temperature data has to come from the Remote Agent, the display in the Miner tab's glitch did not get away until I restarted the AM Remote Agent on the remote rig, please note that Map to system monitoring can only see 2/3 cards as well until the Remote Agent was restarted.
It might very well be that some new kind of driver crash causes the monitoring that Awesome Miner do to not work correctly. Please select a miner and click the System tab to see what Awesome Miner is reporting for the system. When you don't get the temperature readings anymore, are the temperatures listed as 0 in the System tab, or are the GPU's no longer listed here at all?
When using "Map to system monitoring" in Awesome Miner, the temperature readings and more will be taken from the System tab and map that into the GPU list on the GPU tab. This is the reason why Awesome Miner can get temperature information and more even if it isn't reported by the mining software.
What I will do in the next development release is to add a new button "Reinitialize monitoring" on the System tab. Please give this one a try to see if it resolves the problem.
