@Don, it is difficult to say if external would be any better. If the problem is hardware related then it would. If the problem is in the interface between the hardware and applications then no. Both iOS and Android have an abstraction layer that allows multiple applications to receive GPS information. If the issue is in this layer then no GPS will do any better.
As I am currently in Africa and quite busy, I havent really been able to help research any of this. On my flight here I used iFly until we left US airspace with no issues. However, my tablet is still running Android 5.x and nothing newer. I plan on upgrading one of them when I get back. (I always fly with 2 tablets, but I have never had to pull my backup out).
Here are some of the things that would help greatly to troubleshoot this issue. Start by flying (prefereably as a passenger).
1. Run GPS Status or similar app and see how many sattelites are in view / locked. When iFly reports no lock, switch back to GPS Status and check again the status in view / locked
2. See if GPS Status can get a lock and maintain reasonable lat/lon changes without using iFly
3. update agps and test 1 and 2 again
The next two problems I find unlikely, but I did find some other developers who have reported:
4. the problem could also be a corrupt gps cache. I would have to research this for the specific version on how to clear the location cache without clearing the entire cache.
5. Low on storage on your primary sdcard / storage (internal not external).
I am highly suspicious of #4 and #5 as GPS requires very little memory and really no access to storage except maybe to write a temporary file prior to handing off the NMEA records.
I also saw a report that the latest maps application updates broke something. I am suspicious of this as well, however it's easy enough to uninstall google maps updates and try.
If iFly gets a lock and loses it when you switch to another app, then installing an application that keeps the gps running all the time might be a workaround (normally when you switch to another app, Android "suspends" the previous app and it no longer gets gps updates). It's doubtful, but yet another something to test.
Finally I have seen one bug report on Android 7.1 as having a GPS firmware problem...but I did not read the details of the bug report. In fact right now my internet connection is fading so I cant bring it back up...I'm hoping I can get this posted.
Sorry this post is so long, I'm hoping some of the users with problems wont mind doing a bit of testing. It would be of a great aid to the entire community.