Checked all the wiring and now the IR sensor always flashes 4 times but triggers to a value of 538 at two levels, one around 8mm and then again at 1.7mm. In between the value falls below 500. This trigger detection is very repeatable and happens with the PEI bed or white paper or even with a hand. Red LED comes on at both heights and goes off in between

I'm having a problem with an IR probe. I think the issue may be related to wiring but here is what happens. I seem to be able to get the IR probe into 2 modes. Normally it will flash 4 times on startup and probing (G30 S-1) gives me a distance of about 1.77mm. On other occasions I do not get 4 flashes on startup but auto calibration seems to complete though the IR probe never flashes during auto calibration and the results leave the measurement about 5 mm too short in the Z axis. The head seems to travel about 10-12 mm above the bed during calibration rather than the more normal 5-6mm. Does this seem plausible and is it likely caused by a wiring issue? I'm using black painted PEI known to work on another printer with an IR probe.