GPSMAP 66sr - first track anomalies

I took my new GPS out a few days ago, to test it on a moderate hike in a nearby park...

I also got the Backpack Tether along with it, and mounted it on my shoulder strap near the top, so it should have had a clear view of the sky throughout the hike. I set Battery Saver to 2 minutes, and left it with the auto-pause-when-stopped and auto-resume functions enabled. I did *not* select Expedition mode. Battery was fully charged the night before, and still showed as fully charged when I got home after the hike.

I'm enclosing an image of the resulting track... I did stop, to sit and read for a couple of hours, at the waypoint "Coal gully", but left the GPS on, in auto-pause mode. I'm startled by the long blue sections, where it appears to have stopped sampling for some reason... the first three were when I was under trees, though the trees were not very dense, so I would have expected it to stay connected to satellites?? However, the long, blue section in the lower left was mostly in open grassland... Note that the beginning and ending parts of the track *were* under full, heavy tree cover, yet it seemed to be tracking position easily and accurately in those stretches.

Can anyone give me any guidance on what I could do, if anything, to improve its ability to continue capturing track points while I am hiking?? This is one of the primary reasons (besides battery performance) that I replaced my previous GPS...