SSL certificate problem: certificate has expired but browser tells that certificate is valid.

[Neo Anderson]

Yesterday everything was working. Today I got this error message: SSL certificate problem: certificate has expired 
Then I copied the URL from sourcetree directly into a browser window. No issue - and the cert check told me that my cert is valid.

If I switch off the SSL cert validation below options -> git -> it works again.

But that can't be the solution even there have been no other changes taken place on my pc.