I had a Rebuild of my network the other day. I wanted to change some of the things the smart apps were doing so cleared everthing and started from scratch.
I only use the Modes for Lighting room colours etc. However noticed the modes appeared in my Routines for the automatic stuff. the arming of the system via presence sensor (Goodbye!) and the arrivals (I’m Back!). nether of these worked after the clear out, just wouldn’t fire. I then removed the MODE from that Routine and they have fired flawlessly since.
Don’t know if this is a known thing or a weirdness. May help someone!