Do you mine running HwInfo 24/7 can affect hashrate/valid shares and overall work of the miner?
Yes, it can affect overall stability of a system
I have just recently started running HWinfo 24/7 and have not had any problems - so far - but that said it is best not to have anything else running when mining as it could affect the overall stability.
Yes, I've had the same with hwinfo. I installed and ran it and lost 5-10% hashrate. Turned it off, and back to normal.