Identifying iPhone GPS issues

I own an iPhone X, purchased a few months after its release (November 2017). I'm getting close to the end of my AppleCare+ window, and as such have some urgency to identifying whether the following issue is legitimate (and needs to be/can be fixed) or not. I'm not looking for support for the issue itself, but for how to identify/troubleshoot it.

The last few days, my GPS location accuracy has been ... bad. Very bad. I was driving home on Sunday, and asked Siri for directions out of the strip mall I was having lunch in back to the highway; Siri started telling me things that made no sense, multiple different sets of things, and was very far off track (and moving about wildly). My wife, who also has an iPhone X purchased at the same time on the same service, set up her directions and had no issues with drift.

The rest of the trip home I continued to experience far more frequent "course corrections" (while I was driving along a deserted freeway) than is typical - tens of corrections, even in fairly open areas, as opposed to the typical two or three. My wife's phone had nearly no issues.

I also play some location-aware games, and have had multiple instances where they were far, far worse than usual. I'm familiar with normal GPS drift, but this seems different.

Is there any way for me to identify this as an actual problem (as opposed to just normal GPS drift that I'm just noticing more for whatever reason)? An app, a log, something like that where I can either diagnose the problem or collect data on the problem so I can 1) prove if this is a problem or not, and 2) show it to Apple support so they can identify the (hardware/software) problem?

If it's relevant, the issues occurred on iOS 12.4 and iOS 13.0 (but I've since upgraded to 13.1). Never on a beta, always on release versions.

The best bet is to take it into an Apple Store and have them run diagnostics on the device. This won't take long to do, and there'll also be a record of it on their systems.

If an Apple Store (or authorised repairer) is not convenient to you, Apple can also run diagnostics while you're on the phone to them.

Regardless, the diagnostics will identify any hardware related issues on your iPhone and that's really the best way to troubleshoot it.