Need help with a network renovation gone wrong

[SOLVED]

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The switch used was broken. In some bizarre way.

Replacing the switch fixed the problem

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I just recently renewed my home network after my old router started acting up. To replace old gear i bought an usg + unifi uap-ac-lr combo and attached them to the old network in a way described bellow.

Network configuration (ZyXel Antenna/Modem is running in bridge mode)

My problem is that only the UniFi UAP has access to internet. All other devices in the network are unable to connect to internet. Devices other than the UAP are also unable to ping the usg. My guess is that there is something weird going on with the USG DHCP-server or the ZyXel Modem(running in bridge mode). To make matters worse, connectivity of the UAP is weird. Sometimes only devices running Android are able to connect while all other devices are unable to get an ip, and sometimes it's the other way around or so that no device manages to get an ip at all. Wired devices are never able to get a working connection, but they do get valid ip's/configurations.

There is something weird going on with the wired connections as sometimes my computer receives bursts of telegram messages while simultaneously not being able to ping anything. This sudden connectivity (which drops off immediately) happens only with the telegram messages. Also all the ports of my USG somehow show up as "disabled" in the UniFi Controller interface.

Has anyone here encountered something similar or better yet does anyone have any ideas on how to solve this? I have tried: static ip configs, readoption of the USG , connecting my UAP/PC directly to the USG and switching all dns settings from Cloudflare (1.1.1.1) to automatic.

Thanks to everyone in advance