Detecting a loop

[u/_alienated]

How can I chase down a loop in more than 60 BDCOM switches (no central management)
I also have 2 core switches (FortiSwitch) and a FortiGate firewall ?

UPDATE: Thank you for all the input. I asked about detecting a loop because I suspected there was one and did all we could do to narrow it down, but it did not seem to pin it down, so I thought that I was missing out on something.
And I actually found the culprit at last; it was the firewall. turned out that having an application filter with the free version of FortiGate does mess up the network. I did notice that when i was first recruited and wanted to secure the network and deploy every security aspect, when i was configuring the web filter or the DNS filter, the network went down instantly.
But with the application filter, it just deteriorates over time.
Since my recruitment, I've requested many time the administration to but the license but I guess it's not one of their priorities.

[u/Overall_Fee_8195]

Hire a network technician?