Garmin Inreach Explore+ GPS Issues

In most cases, this kind of discrepancy is due to differences in the datum between the two devices. OTOH, a difference of 10 miles is a lot. 

The Explorer+ supports only NAD27 CONUS, WGS83 and WGS84. The latter two are virtually identical. NAD27 might differ by a few hundred yards, but not by 10 miles. Do note that NAD27 CONUS is only entirely valid in the continently US. But I don't know what datums your other unit supports.

The other possibility is a difference in coordinate format (for example, decimal degrees vs. degrees and decimal minutes vs. degrees/minutes/seconds). Then there are other coordinate systems such as UTM or MGRS. You are much less likely to be confused by the use of different coordinate systems because the coordinate formats a different.

Note that WGS84 is the most commonly used datum on modern GPS units. Chances are that the datum/format in use on the iR unit does not affect the coordinates transmitted with an SOS, message, or track point. Those coordinates are most likely sent in WGS84 no matter how the unit is set. To put this another way, the settings on the unit control local display on the unit and inputs via the unit's hardware. Internally, everything is WGS 84 no matter how the unit is set.