AThe Home assistent Cookbook has many articles on Zigbee and what you should do to get a stable mesh. Most common problems are not using an extension cord to keep the coordinator away from interference (e.g. from USB3 and other sources), picking a channel that is too crowded, not using enough Zigbee routing devices and more. The best place to start is probably this cookbook article:
One of the problems is that inbuilt switches are in a bad spot to begin with, inside a wall and surrounded by power cables…