smart poe switch closing down ports

I recently bought the above switch to make my home network a bit neater, has a router going in and a ubiquiti cloud key plugged in running 4 wireless ap's it then has a bout 10 devices plugged directly in and 3 ports going off to un managed switches with the ussual stuff hanging off those, wirelass ap's computers, cameras etc. My old system was two unmanaged 8 port gigabit switches daisy chained together and poe injectors where needed. Now im having problems, i can plug almost everything in but when i come to the last two ethernet cables both going to switches with multiple devices attachedI plug one in ok, but as i plug the second in the first one all the lights on the port go off at both ends??

all cables are ok, I have checked all ip addresses (37 of them) and none conflict that i can find. I have switched off all the meshing on the wireless ap's (each switch had a wireles ap on it.

Ideas please for a none network gurus

is there a feedback loop?, how do i find / stop it?

many thanks, nick

Oh i updated the firmware to the latest (took 4 or 5 seperate updates to do)