EDIT:
I believe that the problem is also present with WiFi passwords. My WiFi password contains symbols like $!& etc. (but no comma!) and the connection cannot be established. My Fritzbox blocks it. If I make a guest account with numbers, the connection is established.
If you assign a WiFi name with a comma It is stored incorrectly in the RPi.
Example: fritzbox7590-2,4 becomes fritz7590-2%2C4.
EDIT: I believe that the problem is also present with WiFi passwords. My WiFi password contains symbols like $!& etc. (but no comma!) and the connection cannot be established. My Fritzbox blocks it. If I make a guest account with numbers, the connection is established.