In this case it's an HD radio broadcast, which is digital.

It's digital, but still in the broadcasters FM allocation. https://en.wikipedia.org/wiki/HD_Radio

It has nothing to do with 5G, which is a cell technology. 5G has low (600-900MHz) medium (microwave) and high ("mm wave"), and is far away from broadcast FM frequencies (USA is 88-108MHz)

https://en.wikipedia.org/wiki/5G

https://www.fcc.gov/media/radio/fm-frequencies-end-odd-decim...

My wild guess would be that there's something in the HD broadcast causing the issue. Something as simple as a metadata field being too long could trigger a bug in the headunit firmware. The HD broadcast spec seems non trivial and largely closed off so it wouldn't surprise me that there'd be buggy implementations.

That sounds likely, given the easier issues.