Long shot here, perhaps?
This boiler has no error codes but flames out with what looks like insufficient gas on a modulated lowish output and purges before restarting.
Placed the boiler in calibration mode and it runs nicely at 100% but flames out when on a lower output %, then a purge and the whole calibration cycle starts again.
This will happen as many times as you let it until you kill the power. No error codes or other indication of a problem.
These Baxis seem to be renown for faulty gas valves and would this be the likely cause?