1200 would indicate default entry with unsuccessful connection to XO server.
I’m not positive, but I believe when the data field is reinstalled you have to re-enter your username and password on Garmin Connect under the Connect IQ data field settings.
Normally, as long as phone is running GC in background, the MPA field should update within a few seconds.
Related topic with something else to try –
I’m using the “MPA and Power - Xert” on Garmin 1030 MPA always 1200 - Support - Xert Community Forum