I wonder if it’s related to this issue that Nebula also has on Synology docker. https://github.com/slackhq/nebula/issues/256
For now, I have a workaround in the form of a script that runs hourly and re-adds the route if it’s missing. I’m wondering though if the device ztwdjclgcv is static or could that change? Here is the script for anyone interested. We have all our client NAS’s connecting to the same zerotier network (with flow rules preventing communication between them), so this may not work for everyone but will have to be customized regardless. I did verify that this works again the 3 NAS’s that were currently unreachable.
EXIST=`ip route show 192.168.XXX.0/24 | wc -l`
if [ $EXIST -eq 0 ]
then
route add -net 192.168.XXX.0/24 dev ztwdjclgcv
fi