GPS Issues - is there better hardware available?

Throughout the past year, my company has been having a lot of GPS related issues. Currently we use the Here2 GNSS GPS and mRobotics GPS. Generally, both work. However, there will often be times that GPS signal is lost or cannot even be found from the start. It doesn’t seem to be a location issue, as we can fly a drone, land it, reboot, and it can lose GPS lock that prevents mission starts. In certain situations, we can have upwards of 19 satellites without having a GPS lock.

This has been tested on base installations of both Arducopter and PX4, so it seems to be a hardware-based issue. (Using Pixhawk 2.1 Cube Black on most builds)

Is there an issue with this hardware? Can it be configured differently, or is there different hardware that we should buy?

We generally fly 5+ at a time and typically at least one of the five will not have GPS lock at any given time.

It sounds very much like an interference problem from somewhere.
What is in proximity to your GPS on your builds?
Having 19 sats and still having a GPS lock is suspicious.
Can you provide a .bin file from one that has lost GPS lock?