Uhm, yes, it’s doing it for every print.
Bambu has a bed mesh MERGING algorithm. This merging algorithm I’m not familiar with as they never fully disclosed it, but the idea is very different from approaches that other firmwares (like klipper, and klipper adaptive mesh probing…). I think it initially started from the X1 series with the lidar, which is of course a different bed mesh system than probing. So how do you combine two different probing results, and how to generate a reliable bed mesh compensation? I guess that’s when they came up with this merging system.
For Klipper systems the newest bed mesh overwrites the previous one. But for Bambu, it would remember two sets of different bed meshes, one as a base model and the other one used to adapt to the current condition with minor adjustments. And for X1C they just use the lidar output as another mesh to merge with. I think Bambu found this method more reliable than other methods and in general practice it looks like to be the case.
Basically, the bed mesh that you did in the Machine Calibration has a much higher priority than the one you did before print. And it would be remembered.
Let’s call the Machine Calibration bed mesh “Base Bed Mesh”. The bed mesh before each print “Adjustment Bed Mesh” or “Adaptive Bed Mesh”.
ABM doesn’t “overwrite” your BBM. But it overwrites itself between each print.
Bambu uses the algorithm to merge your BBM with the ABM. But if the algorithm fails to merge them together, then it would try probe again. This time it would temporarily override the BBM as a failure back up. Or at least that’s what it seems to be doing. But the result can be very poor. So I’m not sure about this part (how it actually handles when it cannot merge the two bed meshes). All that I’m sure is that the BBM would only be overwritten with the Machine Calibration process.
Now, since you have changed a plate, your BBM no longer matches what it used to be. So a failure on merge is gonna happen, and because before print probing process only generates ABM and it would not overwrite the BBM, the next time you lunch a print it’s still gonna fail.
Fun fact: I miss the lidar on X1C. If you don’t swap plate on X1C, you can essentially turn off the abl probing before print and the lidar would take care of it 99% of the time.