I have been reading a lot on the forum but I haven’t found any info on this particular problem. I’ve checked the zigbee and wifi channels and my zigbee network (19 nodes, 9 routers) but that seems to be okay. The devices (and batteries) are new. I just can’t figure out why the would just stop responding.
The motion sensors seem to be in the network still:
But they just freezed:
So if you know any alleys that I could try, please let me know! 
