Activities cannot be saved often because of some unknown errors

That's when it didn't give a "Lost Satellite Reception" error, which is common on these.

I understand that GPS is not extremely exact and prone to error especially on hiking trails, where tree leaves and mountains can affect the signal, however, an error of one half mile over a 4 mile hike is unacceptable.

There are a few major reports of dead systems and errors in GPS / Timing.