Start by looking through this. A flakey Zigbee network on ZHA will likely be flakey on Z2M too. Zigbee network optimization: a how-to guide for avoiding radio frequency interference + adding Zigbee Router devices (repeaters/extenders) to get a stable Zigbee network mesh with best possible range and coverage by fully utilizing Zigbee mesh networking
Likely caused by how you set up the automations that trigger the notifications. Can you paste the automation as preformatted yaml? use the </> button to format the yaml.