I used the BLTouch V3.0 on my Ender-5 with the Creality board with the Marlin 1.1.x version. I had to add some additions to the Marlin source at the time because V3.0 wasn't working with the stock firmware, but once I added these additions it all worked out perfectly.
I did run into something similar to what you describe, but in my case I sometimes had an air-bubble trapped between the magnetic build plate and the magnetic Z bed. As long as I made sure the magnet was securely down without a bubble, I never ran into air printing again.
I didn't have any special code for my start g-code. I was using Cura 4.0 with the BLtouch, and only had the G28 to home and then G29 to probe. I didn't have any M280 like you have on any of my start code.
I've since then replaced my Creality board with the Duet 2 Maestro, and even on that board the air-bubble can cause it to air-print every so often too.
Edited 1 time(s). Last edit at 08/18/2019 04:51PM by PDBeal.