After further checks the issue appears to have been documented on this page :
https://www.litespeedtech.com/support/wiki/doku.php/litespeed_wiki:plesk:webmail_500_error
problem resolved.
The MBstring is already available and installed :
rpm -qa | grep plesk-php74-mbstring
plesk-php74-mbstring-7.4.33-1centos.7.221109.0743.x86_64
Any other clue ?
Hello
The issue appears on its own since introduction of the latest version 18.0.51 we have been getting these cases related to litespeed and roundcube, we tried checking if the issue is related to CageFS but it does not appear to happen due to that.
Swtiching to apache resolves the issue...