check out the following thread: https://community.smartthings.com/t/many-zigbee-devices-randomly-go-offline-network-very-unstable/264519/94
I recommend you open a ticket with ST support, send them logs from your hub and give ST access to your hub. Details on how to do this are here: https://community.smartthings.com/t/aeotec-hub-will-not-stay-connected-to-zigbee-devices/265272/10
tagging @nayelyz