Did you try changing the certificate folder permissions? Make sure your webserver user has write access to the folder. You should have the folder set to 755 to be able to write there.
I’m not sure why I’ve had to do this sometimes, but there are times when the key files fail to write out that I’ve had to clear the oauth2 private keys in the database. They are found in the keys table and you may need to delete the oauth2key and oauth2passphrase entries.
One thing I would mention is that I hope you are working off of master because you are doing development. If you are upgrading a production machine, its not a great idea to work off of master as there are lots of unstable features that could mess you up. I only mention this since you said you ‘upgraded’ this instance.