I finally have the solution!
However strange…
I would like to point out that I have always correctly displayed the TFT update procedure on the screen.
As per the screen posted previously, the installed version was v27.x Feb 15…
which unfortunately is the same name for both version: with m420 bug and the one without.
After reading this thread:
I had the suspicion that the TFT actually wasn’t updating and after installing the version present in this thread, which changes the value of the date, I realized that it actually wasn’t updating!
I formatted the SD with SD formatter, nothing… updated with power off and reset mode, nothing.
The files changed names in the SD card but the firmware did not update.
So, I changed the SD card and the firmware updated successfully and the M420 error disappeared!
I don’t understand why that SD card, which worked correctly for at least 2 updates, created that “fake update”.