GPS accuracy hardware or software problem?

1. What is the problem? Be very detailed.
ODK Collect reports an accuracy of coordinates that never gets better than 3.9 metres (obtained consistently) despite thresholds being set. From initial analysis, this seems about right. Using Doogee 68Pro rugged phones, which have internal GPS linked to GPS/GLONASS/BAIDOU/GALILEO systems; other GPS applications display sub 2-metre accuracy levels. When accuracy thresholds are set in the form, Collect keeps on looking until the user interacts to save, always producing a report of 3.9 metres. When there are no thresholds set, Collect immediately saves the coordinates at the point that the accuracy slips under 5, producing a range of readings between 4.7 to 4.9 metres. Not sure whether this a hardware or a software issue? If the former, has anyone used Doogee phones before? If the latter, is there something we can do in ODK to improve accuracy?

2. What app or server are you using and on what device and operating system? Include version numbers.
Hosted on Digital Ocean, managed through Aggregate & Postgres databases. Likely culprit is the Doogee 68Pro phones running Android

3. What you have you tried to fix the problem?
Changing thresholds in the forms

4. What steps can we take to reproduce the problem?

5. Anything else we should know or have? If you have a test form or screenshots or logs, attach below.

The documentation for the location widget describes the accuracy measurement:

The accuracy radius is an estimate of what Android calls the radius of 68% confidence: there is a 68% chance that the true location falls within this radius. This is an estimate reported by the Android system based on the available sensors (GPS, network, etc). The accuracy radius itself may be more or less reliable depending on the sensor(s) used and current conditions.

I wonder if it may be possible that other apps are calculating the accuracy in some other way (resulting in a different accuracy measurement)?

Also, have you read the documentation on Improving Location Performance?