SOLUTION.
There are several solutions in the posts above, none of which worked for me. But I found a solution for my A1 and A1 mini that both developed this problem. I changed my slicer from Bambu Studio to its big brother Orca Slicer. Orca is almost identical but has several calibration settings Bambu Studio does not - notably the ability to adjust the z-offset. Changing the g-code in Bambu Studio does nothing due to the A1 series’ autocalibration.
In Orca Slicer select the printer default presets (the box next to printer selection in the Preview tab). In the next window set the view to advanced. In the General tab there is now a setting for z-offset. Bambu Studio does not have this setting.
Orca’s default z-offset is 0.00mm. Increasing the value increases the nozzle distance from the print plate. After a bit of trial and error I found that the new z-offset should be +0.2mm for my A1 mini and +0.35mm for my A1. Your settings may differ.
Good luck, I hope this solves this very annoying issue with the A1 series for you.