Total ascent incorrect

Where do you get the 1050m from?

From OS maps (mapping tool) and also friends GPS who was on the ride with me gave similar.

Also when corrected using DEM data in connect it corrects it to about 1050m.

What mode is your altimeter/barometer setting and how was the weather?

I have the altimeter set to

Auto cal =on

Sensor mode =Auto

I have the barometer set to

Sensor mode =auto

The weather was a nice sunny day with little variation in pressure.

Did you have any pauses in the activity that was more than 5-10minutes?  

Did you have on longsleeves that was covering the watch?

Did you have your phone with you and connection enabled from phone to watch?

Do you make a point of syncing with phone before you head out for a ride (possibly helps with auto calibraiton based on location).  

Do you sweat a lot?!  Do you shower with your watch off?  Sensors can get clogged up a bit with sweat/gunk... usually watches you've had for awhile.  Recommendation from support is to do a soak of watch procedure of some sort to flush sensor of salt and debris.

Pauses/weather/temperature and phone calibration checks can all effect elevation reading.  If you look at rides/runs that are very cold (usually most prominent) that have indoor stops (coffee/gas stations / brewery etc)... and look at the elevation graph, you will notice large changes (cliffs) at that location due to the temperature effects on the sensor.  Similar effects will happen when going from shaded river bottoms where its cold... quickly into a sunny area... not sure why it isn't temperature calibrated and possibly cross referenced with the watches map elevation data... maybe it is now on newer watches?  

This is the newest flagship forerunner

I would rather trust baro based altimeter rather that readings from your friend's GPS. OS map is a crappy tool in terms of measuring altitude - for example, it shows that my local hill is 5 m tall whereas it is 31 m high.

It's funny you write this. I don't have any experience with OSmap, and it doesn't even matter. ANY total ascent/descent "calculation" is... well how do I put it... an almost arbitrary number. There's a minimum I guess (which would be somewhere around the altitude difference between the start and end point, or maybe the difference between the min and max altitude on the course), but from there probably you could get almost ANY number (kind of "endless") similar to how you can't measure the coastline of any island country...