Another Bed Levelling query - very strange behaviour after Firmware upgrade

Ok… so I read through all the firmware updates and purposely have been hanging fire from upgrading as i had a pretty good know baseline i could work with. Ive also read pretty much of all the bed levelling threads too some great info in there @Tone

So upgraded to 1.10.1 from version 1.8. Rebooted… Ran calibration which worked… though interesingly the nozzle is much closer to the bed when doing the final manual calibration than with 1.8 (like about 8mm nearer… relevance will come in a minute)

Started a print of a Gcode file that printed fine yeterday with 1.8 and the nozzle was very well rammed against the bed… so quickly tried to do an offset to lift it a bit and it behaved weird and ended up diving further down and realllllly gouging the bed even though i was going up…

Anyway upshot is Ive had to put a G0 Z7.7 into my Gcode that worked yesterday, followed by G92Z0 to basically shift the Zaxis origin up nearly 8mm so that it actually prints correctly.

What is going on?! - just in middle of a print now that seems to be working ok so will do a M420 V later to get the bed mesh points

Ok… been delving around all over the place for this in the src code for firmware messing with offsets, axis offsets etc, saving in EEPROM etc… God knows what was going on… a gremlin in the software somewhere or firmware or issue or eeprom setting causing a conflict. I did do a G1092 and define a 10 point grid mesh but all the values are around the 8.8 to 9.15 in the M420V command which is very similar to the values i had in my mesh compenstatio with previous firmware. So not obvious what happened yet but one side of my bed certainly felt the pain

Could someone whos running earlier firmware do an M503 and tell me what their Z offset value is… I’ve ended up putting -7.5 in there so my line reads which fixes it. But not sure its fixed in the right place but it does sort things

M206 X-19 Y-10 Z -7.5