I see similar issue reported by someone updating to 17.01.1. In my case I updated my WDR3600 from 17.01.1 to the latest snapshot r4165-c7ee30d. On 17.01.1 LuCI was running, on r4165-c7ee30d it does not.
I can ssh in and I have network access.
Should I file a bug for this or is it already a known problem?