Neverlost definitely has problems in heavy rain. During my last rental in BOS it cut out in heavy rain and started working immediately after the rainstorm in the same area.

For GPS to work the receiver needs to have unobstructed line of sight to 3 satellites.

Tall buildings easily obstruct satellites, and a large concentration of raindrops weakens signals (ever watched a satellite TV channel in heavy rain/snow?)


An inexpensive nav system (like Neverlost?) relying on full-time availability of GPS signals will always have such problems. An expensive one with accelerometers/gyroscopes to take over when GPS signals are not available will work in tunnels, parking lots, city centers, and rainstorms.