So, I had one of these (a 100/30, also in the HQ2601 serial range) as an RMA today, same symptoms of not recognizing PV input with a known-good known-polarity input, and discovered that Victron has added a PV relay control to these units. I have no idea when it was added, and it’s not documented anywhere yet, but seems relevant to the OP here as well.
Get into the Device Info page (follow these instructions 5. Configuration and settings) and if the PV relay has tripped, there will be a button there to click to reset it. Once it’s been reset, the button disappears (thus I don’t have a screenshot of it to share).
In the case of the unit I had here for an RMA, the unit immediately began responding normally and charging as expected once I’d reset the relay.