I'm not sure what is going on, we know
@toolfolks did a clean install of Debian and FusionPBX and has the "Connection to event socket" error.
A netstat -anlp | grep :8021 shows that the socket is not available and fs_cli does not connect, but FreeSwitch is running and shows a clean start up, but is not producing a log file. This was over the phone, I don't have access to the machine. My guess is that for some reason mod_event_socket (and possibly mod_logfile) is not loading.
We suspected that the FusionPBX install may have been broken but I have just built a clean Debian 10.2 VM in the data centre and installed FusionPBX from master (4.5.13) and I cannot replicate the problem, it all appears to work fine.
I would welcome anyone else's thoughts on this.