Uptime monitoring lead to “weird” discovery

Ok so weird thing happened today, I had discovered a service called uptimerobot which as it’s called it tracks your server up/downtimes, alerts you when things go south. So I went ahead and set myself up with an account and started setting up my sites in there and soon enough realized I have a 503 service unavailable error on 3 of my 6 sites. It is my understanding that error 503 means a few things namely with interruptions/connections but here’s the weird; the sites aren’t down! Even more weird is these same ones are the main domains attached to individual hosting accounts and the sites showing as online are add-on domains, 1 per.
The one other thing that I need to mention is that all 3 down sites are multisites, others are standard single installs.
I have WordFence installed across the board and the settings are identical, nothing blocked to my knowledge, have also tried disabling plugins that do redirects (multilanguage setups).
My host doesn’t seem to understand much of what I’m saying seeing the 503s are coming from site that can be browsed. I did explain the uptime monitoring situation thinking it might lead to better diagnosis but to no avail.
Another issue I’m having with the host is that all 3 accounts seem to have an issue displaying error logs (cPanel > Errors), I see the big text area, just stays there without being populated, on hover i get a red circle with line across it.
So what is it that could send the uptime crawlers empty handed back where they came from is beyond?

Thanks for reading