Resolved
due to firm ware upgrade i suspect my 4GB of ram was not enough to run more than 6 x 1080 Ti. as it became more efficient.
i updated bios still not able to run more than 6 x 1080 Ti.
fitted another 4GB of ram =8GB total. now mining happily (the heating is back on)
nichhash is mining lyra2rev2 @ 533.000 MH/s

i found i needed to remove the GPU that are plugged into the M.2 slots.
currently running 6 1080ti happily. nothing out of m.2 slots

I have Asus STRIX H270F i also had 8 cards mining for 6 weeks when nicehash updated to 2.0.2.2 or when windows updated end of May 2018. i cant get m.2 slots to mine. they are recognized but instantly stops mining on nicehash and others.
2200w = 1200w x1 & 1000w x1
8 1080ti
i have not changed the bios to the above mentioned. i will check and update.

I've searched to the best of my ability. I'm sure I've overlooked something simple. but Nichash attempts mine in never-ending loop fault.
nhmp  |  read: End of file

Connected to nhmp.hk.nicehash.com:3200
nhmp  |  Subscribed
nhmp  |  Disconnected
  nhmp  |  read: End of file

thanks