Has anyone ever seen wacky data recording like this?

I recently noticed strange flatlines in the HR records on my watch (6x pro solar). Looking back there were weird inconsistencies for nearly a month. Crazy HR and step recording like i'd been running all day or not moved at all, amongst others.

Garmin support have been great on helping replace, but did anyone else ever see data like this?:

Activity: A run in one direction, followed by a short stop (at a shop) and run back to the initial location. The pace is correct.

Note the HR starts part way through. The temp also starts later at a different time. The cadence records movement but not actual cadence until later, also at a different time 

https://connect.garmin.com/modern/activity/5880516229

Daily activity is missing chunks of data (such as sleep or movement or heart rate or steps way high or low) or flatlined like:

connect.garmin.com/.../2020-11-29

or

https://connect.garmin.com/modern/daily-summary/2020-11-26

I tried the 12.77fw which seemed to fix it temporarily (as did the run in the first link above) but it soon returned to intermittent data again.

Factory reset did not resolve either, nor did disabling activity tracking/hr detection, power cycle and turning it back on etc.

Normal activity (one day before issues started appearing) for reference: https://connect.garmin.com/modern/activity/5727863683 

Interested if anyone else ever had this.