Fenix 7XPSS GPS tries to "lock on road" even if more than 100m away.

Settings->Map->Lock on Roads

sets up the default system settings but each individual activity type can follow or be set differently.  If I recall (been a while), for some dumb reason the default for 'Run' based  activities is set to follow roads so 

Settings->Activities & Apps->Run->Run Settings->Map-> Use Sys Settings->Off or On  Turn Off and the additional options become available including 'Lock on Roads'.  Check this to see what it is.  If using something other than 'Run' same process.

I have tried a bunch of things and nothing seems to work. I have since had a random glitch every other activity. Usually within the first 5 minutes or so but not right at the start. Here is a 5K run on which the glitch added 150m distance and spoiled the entire pace record with a bunch of garbage PRs. connect.garmin.com/.../14013117181 . 

No tree cover with GPS setting at All Systems.

On Tue 13 Feb it glitched out in a similar manner when I started cycling. https://connect.garmin.com/modern/activity/13946534240 Again, open road with minimal cover.

here it has glitched out on 11 feb while running. Agreed that there are trees but I have run this route hundreds of times with no problems using my VA3,FR935,FR955.. connect.garmin.com/.../13917617283

If you are sure that the specific activity (regardless of the global setting) is not 'lock on road' - which does not really look like the issue, I would contact Support, - or take it back to point of purchase if it is new.  A little bit of tree cover should not cause that path.

yes the first time it seemed like a lock on road but later on the glitches are completely random. I contacted support they said they will investigate and get back to me via email in a couple of days. 

I've seen cases when the watch randomly changed an activity setting without that being reflected in the settings UI.

For example, once it switched the distance unit from miles to yards, but when I checked the settings it was still showing it as miles. It took me awhile to figure out. The fix was to switch the distance unit from miles to km, then switch back to miles. What I am trying to say is that perhaps in your case it got flipped to "lock on road" even though it doesn't show that in the UI. Also, I should mention that I've seen similar reports regarding locking on road from other users on Reddit.

It is mind boggling that bugs like this are possible! 

Today's GPS glitch. Last two glitches both happened ~2 minutes into the activity.