Admin Password refused I have got a slightly strange issue. The other day I logged into my macbook without problems. It went into sleep mode, I tried in the evening to log in again. My password was refused. I reset the password via another admin account. I was able to log in, but not to update the keychain. Also checking Keyboard Settings.

I ran first aid. No issues. I tried recovery mode with first aid. no issues.  I did recover one of my backups, my password was refused, I reset it, key chain update worked. I was able to access the key chain but not my "Safe notes".
After a day or so, again, my password was refused. Again resetting my password. keychain did not update the password.

Also tried another keyboard, with no luck. In any case, I was running Malwarebytes, but everything is clean.

Do I really need a clean install?

Do you have any other ideas how to solve this issue?

Thanks a Lot in advance!

(High Sierra)
I would suggest going to an Apple Store or calling Apple Support.  They will be able to go step-by-step to help you find out what the problem with your Mac is and fix it.