Xbox one S app crashes on startup

Server Version#: 1.21.3.4014
Player Version#: 2.65.1.70

Xbox one S app worked perfectly until 2 days ago.
Then, for no apparent reason, it started crashing on launch.
I get the big logo, then back to Xbox home.
Restarts/full shutdowns, uninstall/install cycles, rollback to previous server version - nothing.
Server logs do not include any useful info apart from some SSDP related lines.

Any ideas?

One Xbox update later… still nothing