After Update to 7.13.2 system SMTP TLS not working anymore

We updated from 7.12. ESR to 7.13.2 some days ago. Before this update everything worked well (using gmail with TLS).
After this Update the system notifications (e.g. Workflow, call reminders, etc.) are not working anymore.
Admin → email settings → SMTP via SSL or TLS is blank. Settings to TLS will not saved - after reload the field is blank again.
The personal outbound emails (also via gmail) are still sending via TLS - only the SYSTEM mail is not working.
Any idea?

To fix SSL & TLS blank issue, add one line code in the below file as shown in below screenshot.

File Path: modules/EmailMan/views/view.config.php

Line No. 191

Code: $mailSmtpSsl = (int)$mailSmtpSsl;

SS: Screenshot by Lightshot