They do not like advanced WU's. I wouldn't ever try to BETA tag the M40's. Interestingly enough they have CUDA 5.2 and I have had them run the advanced units successfully, but is sporadic. When I have the time, I will need to do a deep dive on their drivers, I had loaded the CUDA drivers from Nvidias site, but they range from 7.5 to 11.2, Will have to play with them more to get better stability.
Basically, they have been running OpenCL instead of CUDA, which is weird because they have run CUDA before. It might just be a driver thing for sure, as I swapped MOBOs last night. Might need to clean install OS and Tesla Drivers. Looking forward to getting the bifurcation cards as well. Also as previously mentioned, I think 2 of the cards are dying. Make sure you get these tested asap to make a return if needed. I also have 3 more coming tomorrow.
https://www.techpowerup.com/gpu-specs/tesla-m40.c2771
Lastly, the cards would probably benefit big time from new thermal paste, considering they are 6 years old at this point and what we've bought has probably been working non-stopped in some data center somewhere. Will need a free weekend and A LOT of beer to get that tall order completed.
At the end of the day, the numbers don't lie. If you can get them working right, for 120$, the M40 is hands down the highest PPD potential (Maybe not the most efficient) card on the market. They don't mine well, so they aren't being bought up by miners.