An update on this issue:
I've gotten my hands on a Fire (5th gen) with FireOS 5.7.0.0 and have been able to figure out what the issue is with version 4.5.2 of my app. Version 4.5.4 does in fact fix the issue (as confirmed above).
The issue should only happen if you have a Fire device on FireOS 5.x with a recent version of WebView (i.e. 100). If your Fire has FireOS 5.x with older WebView (i.e. version 59), or if your FireOS version is anything other than 5.x (either older or newer), then you should not have a problem with version 4.5.2. If you are experiencing the issue though, you will need version 4.5.4 of my app (or any version other than 4.5.2 - the issue is specific to that one).
Unfortunately, Amazon is still dragging its feet clearing up my Amazon App Store submission status for both Full and Basic versions of my app, so as of this morning, I am still unable to post the fix to that app store. I will let you know when I finally release 4.5.4 with the fix.
If you have access to other app stores like Google Play, or if you are OK with side-loading, I've posted details about those options above.
Sorry for how long this is dragging out, but I'm not sure what else I can do other than communicate with Amazon through public forums to try and get some focus on the issue - which I have been doing but with as of yet limited success.