When I go
Top > Service Director > Plesk Manager > Domains > domain.tld and press "Log in to CP" I receive an Application Error and in the corresponding problem report there is the error
Can't load plesk client cache!
The issue affects many Plesk domains in Status Synchronized ( Active ).
There is a task named Plesk cache update that gathers information from Plesk nodes into PBAS.
It fails by timeout as it follows from
[2015/03/09 14:12:19] [ERROR]  [HSPC::Taskman::call_task] <=== Task #37 failed locally: 500 read timeout at /usr/lib/perl5/site_perl/5.8.8/HSPC/Taskman.pm line 289
Increase the Plesk cache update task timeout it is described in
and restart the task.