Upgraded from 4.3.7 manually downloaded and installed CubeBlack 4.5.7 from ArduPilot firmware : /Copter/stable-4.5.7/CubeBlack
I get see this message:
EKF3 not enough memory
QGC - on connecting the board, says bootloader version=5 Board ID = 255 and Flash Size 2080768
can it be that I got wrong build?
Try this one:
CubeBlack
those two .apj files are equal (both when using md5sum and cmp commands.)
Any other ideas?
-Lua scripting is not enabled. I cannot think of any reason for this to happen.
Not likely but is EK2 still enabled.
There are no EK2* params anymore.
And EK2 was disabled long before the upgrade (EK2_ENABLE,0)
There are 300 SRTL_POINTS - which I believe is default.
FWIW: I also re-flashed the firmware automatically selected by QGC.
Why do that. Use Mission Planners load custom firmware option and select the downloaded .apj.
Could be the same.
Yea there are, they are disabled. It goes away in 4.6 There was a time when updating from an old version this was still sometimes enabled. Not the case here as you say.
My first flashing was manual downloaded .apj because first attempt on auto-download by QGC failed. The second was just … to eliminate any potential chance of bad data aligning with a checksum and the universe 
I am not involving windows in things that fly, hence no “mission planner”.
Use the custom build server and disable some stuff.
Good idea, I have also Cube Orange+ that I could throw in, but at this point it would be fun to figure out what’s causing this.