LTHR changing itself?

Do you have two devices? I found my FTP kept changing but it was because I didn't set my FTP on the other device despite setting it correctly on both devices in Garmin Connect and syncing. 

Check your setting on GCinterwb

There's settings for auto update for MaxHR, LT and FTP.

If the LT setting is enabled, it will update if LT is detected during a normal run using chest strap, and there's no need to do the guided LT test unless you struggle to get detection from your normal training.(I believe it works only when using the native 'Run' app however) You will be notified on the watch after ending the activity if LT was detected during the run - even if the value(s) didn't change.

https://www8.garmin.com/manuals/webhelp/forerunner945/EN-US/GUID-0EDC68E3-D886-48D2-B624-AA634739B421.html

Thank you for the  reply.  I never saw a notification regarding LT detection which is why I was surprised it changed in my settings.  Perhaps I just missed it.  Do you know if the notification happens immediately after pressing pause, save, etc or after some time?

I believe it pops up after you hit save, and I think maybe it shows only for a few seconds before it goes away without any button presses, so it can easily be missed.

However - I you flip through the pages in the Training Status widget you'll find a page showing your current LT pace and HR and which day/date it was detected. You can also see this information in the performance section of the Connect app.

Learn something new everyday, I didn’t know this either! Thanks!

does it also update the HR zones accordingly?

It will update the zones if you say so when it asks. I did a run recently (Friday) that said it detected a new threshold and asked if it could update the information, I said yes! My zones didn't change as the LTHR stayed the same but my pace had changed.

Thanks!