Fired up an old rig that hasn’t been used since ETH mining went away. It’s really just a hobby but whatever… I set it up to mine ETC and all was fine then I noticed one of the 580’s wasn’t recognized anymore. Checked cables, etc… Replaced riser and it came back and all was well. Now I am seeing invalid shares on that card. Same setup as the other 580, only difference is the mem type. Any suggestions? Other than new cards? lol!
try very conservative clocks and see if it continues to have errors. if it does you may need to switch to a core only algo instead if you want to continue using it
What would you consider conservative and you do mean the core clock that is now at 1150?
What is a core only algo…
Remember - it’s a hobby and I am learning the lingo 
very very low mem and core clocks, higher voltage, work your way up/down if its stable.
etchash is a memory intensive algo, some core only would be sha256d(radiant) kheavyhash(kaspa), blake3 (alph) ironfish etc etc