What is the terrain like? Open skies or a lot of trees? I am a mostly retired land surveyor and have been using gps for years, and to just get a rough location, maybe within a few hundred feet, gps will work in the trees. To get a more precise location you need at least some open skies. Also some gps systems get corrections from different sources. Wass used to be a common one and in that case it was a single satellite broadcasting the corrections, if the satellite was blocked you location would degrade. Some corrections also are a radio broadcast that could be lost. I’m just guessing here on some of the possibilities.