Signature auto enter when typing

Some of our users complaining when answering a mail or creating a new mail the signature automaticaly enters every letter they type. This does not happen every mail, so it is random. Even if I open the same mail again, one time it does other times it doesn't show op.

When they press enter or backspace its back to normal and the bug stays away for that specific mail. 

If you don't fix it and send it to the receiver its looks totaly normal. 

I have also already created a new signature because I thought it was an HTML problem, but the problem remains.

This is happing with version 16.0.16924.20054 and 16.0.16924.20042. i can't check older version because everyone is up to date.