Temperature Recording has been stopped Since V12.20 Beta

You need to switch ion the record temperature setting under the activity setting . It likely got defaulted to off with the FW upgrade . Look under Run activity setting as an example and you will see the option to record temperature there . Make sure it is ON

Yes , that's one more issues that started with the 12.23 firmware update 

On my device the switch is on, but it only shows my Tempe sensor which I don't wear on runs; it was recording OK with the 11.12

Mine works fine since I made sure the settings on each activity was turned on 

On mine is on; I can't turn it off.

So that seems to indicate it is connected and records with the tempe 

maybe make a copy of the activity and name it without Tempe and try set it up differently ?

You are right. It turns off by default in all activities so I have to turn it on one by one. It is really an unnecessary change which causes inconvenience.

I have a Tempe sensor too, but I only use it for hikes. However, it seems that this change assumes you use it for all activities (even open water swimming!). If you're not paired, it doesn't record anything - I would expect it to default to the internal sensor. Anyone else seeing this behaviour?

I had already posted this behaviour 19 days ago in the beta bug report forum. Please vote for it there.

forums.garmin.com/.../temperature-data-and-graph-missing-in-run-activities

"If a Tempe is paired with the 955, you can‘t disable tempeature recording.

And if the tempe is not connected, there will also no temperature recorded. Before this beta temerature was always recorded. If the Tempe was connected, it shows the data of the tempe, otherwise the data from the watch."

Done.