App rejection due to files grey out/ non selectable from Apple's testing

From Apple
Guideline 2.1 - Performance

We discovered one or more bugs in your app when reviewed on Mac running macOS 10.15.4.

• .GPX files are grayed out and non selectable in Open dialog. (Please see attached screenshot)

• Selecting File/New menu displays an error. 

Hi all. My Mac app, which is currently on the Mac app store, had its update binary rejected. The above is bugs found by app review, out of which the second bug is something I could replicate and identify (totally unrelated as it only has got to do with me not disabling File > New menu even though my app is only a viewer, not editor), and is one that I have already fixed and ready for the next submission.However, I wanted to get both issues sorted and submitted at once.

From Apple's end, it was reported that the files of supported type (.gpx files) are grayed out and cannot be selected. However, I was unable to replicate the same issue with the Macs I have. After some back and forth with App Review, they still couldn't open them (they tested their own and my files, even gave me screenshots) while I could open both their files that they shared and my personal ones.

Here's the document types settings in my Info.plist:

Code Block     <key>CFBundleDocumentTypes</key>
		<array>
				<dict>
						<key>CFBundleTypeExtensions</key>
						<array>
								<string>gpx</string>
						</array>
						<key>CFBundleTypeIconFile</key>
						<string></string>
						<key>CFBundleTypeName</key>
						<string>GPX File</string>
						<key>CFBundleTypeOSTypes</key>
						<array>
								<string>????</string>
						</array>
						<key>CFBundleTypeRole</key>
						<string>Viewer</string>
						<key>LSHandlerRank</key>
						<string>Default</string>
						<key>LSItemContentTypes</key>
						<array>
								<string>com.apple.dt.document.gpx</string>
						</array>
						<key>NSDocumentClass</key>
						<string>$(PRODUCT_MODULE_NAME).Document</string>
						<key>UTTypeConformsTo</key>
						<array>
								<string>public.xml</string>
								<string>public.text</string>
								<string>public.data</string>
								<string>public.item</string>
								<string>public.content</string>
						</array>
				</dict>
		</array>

Since the app's first version is already on the App Store, I assume it has got to be something done in between the two versions, but couldn't find anything off, as I did not touch the codes relating to opening a document in between, as far as I remember.

Anyone here has any clue or any probable flaw with my above setup? Could it be some other entitlements thing or sandbox thing that I missed or accidentally toggled off?

Any help would be appreciated. Thank you.