Cannot establish proper connectivity to Paired Server

Hello Members,

I've set up a reload server with 4 domain and 7 po jobs, all collector model. Domain jobs start at 18:00 and finishes always successfully. Po jobs start at 18:10 and only 5 of them finishes successfully, 2 of them fails with "Cannot establish proper connectivity to Paired Server". Which one fails and which one succeeds is random. I assume, that there is somewhere a software limitation, that allows only 5 parallel collector backups jobs but I cannot find it, and this drives me crazy.  I went through all sort of reload parameters, changed everything but nothing helped. I've even changed sshd_config to allow 100 concurrent sessions, no luck. My next step is to shift the jobs, so that less than 5 of then runs at the same time, but the lengths of a job cannot be predicted, so eventually there can be more than 5 jobs running. Can somebody help me?