Andrey,
we observed the same.
If you don‘t use VPN with the edges everything will be fine. The tunnel is established but no traffic is going this way.
A workaround is, to not install R80.20 policy to the edge device or the LSM-profile if used. But with this workaround you can‘t change anything at the policy for the edges.
We used these, because we were on the way of replacement of the edges with 14xx appliances. This worked for us for an half year, now we replaced all edges and we can change the policy for the new 14xx.
We never opened a case for this.
Wolfgang