I just noticed that the 11 activities I've recorded since 17 May with version 23.20 do not have elevation data.
All the activiites with the prior version include elevation data.
This is in addition to my lack of notifications since installing version 23.20 (and yes I've rebooted both watch and phone, and paired / unpaired several times)
My watch is almost 3 years old so i doubt it's covered under warranty, but as far as i can see Garmin just broke my perfectly good watch with a malformed over the air update.