Importing a jpg with metadata in XMP sidecar (from FastRawViewer) - LR seems to ignore the metadata

I just imported several jpg files to which I had added metadata in FastRawViewer which was stored in xmp files. 

When I imported these files to Lightroom Classic, the metadata was not read with the files.

I did a test of the same metadata fields, also in FastRawViewer, but for a .NEF raw file (and xmp) and that metadata was successfully imported into Lightroom.

I've not seen this problem when importing jpgs with metadata added in PhotoMechanic, but It looks like PhotoMechanic actually edits the jpg to add the metadata fields and does not create an XMP.

MacOS Sonoma, Current Lightroom CC updates, FastRawViewer 2.0.8

In summary,

FastRawViewer:  Raw+XMP - Lightroom reads the xmp

FastRawViewer:  JPG+XMP - Lightroom appears to ignore the xmp (I'm not shooting Raw+JPG, these are only JPG frames)

PhotoMechanic:  Raw+XMP - Lightroom reads the XMP

PhotoMechanic:  JPG file modified - Lightroom reads the metadata from the JPG.

Has anyone used Lightroom to import JPG+XMP, what is supposed to happen, and, and any ideas how to fix this?

Thanks,

Don