One thing I've noticed with OnX is that the tracks don't always exactly follow the trails I've hiked. They can be as much as 10 yds off from what I can see using the satellite photos. Normally 10 yds is no big deal. If I can't find my way within 10 yds I'd better stay home. However, if I had to use an inaccurate waypoint to mark a dead elk in heavy cover it might be a different story.
Using my Garmin Montana with a HuntX chip for geocaching, I've found it accurate within 3'. I haven't yet used my phone and the Garmin side by side to check for the the phone's GPS accuracy.
This is a guess, but that may just be differences in the mapping data...not necessarily an error on OnX's part.
The satellite photos may have been mapped using NAD 83 and the OnX maps may have been developed using WGS 84, or vice versa. Likewise your GPS/phone settings may be set to one or the other, where the map or overhead photos you're looking at was developed using different data.
It likely doesn't matter much as you mentioned, but I have had this issue finding small cadastral survey markers that have been overgrown with brush.
