New Switch brings network down.

I have 8+ unifi switches and just bought a new USW pro 24 POE (have others of that model running). When I connect port one to another unifi switch it brings my entire network down. No ping to 8.8.8.8 or any access to the internet. Once I unplug it the network comes back up in 1-2 minutes. This is a brand new switch. Luckily I have another network and was able to adopt it immediately. Any idea what be going on? I thought STP but that doesn't make sense to me. Thanks