The certificate is ok and ssl was working. De server also have plesk 17.8.11 (plesk onyx).
After upgrading to plesk 18.0.21 (plesk obsidian), webmin won't start anymore with ssl enabled, ssl disabled works fine. The log gives the error:
Failed to create SSL context : Invalid argument at /usr/libexec/webmin/miniserv.pl line 4383
As far as i know: plesk doesn't install, change nore delete anything from perl.
Access to the server can be provided if needed.
Kind regards Jan