Keep gupdate.gcd on-board after update?

[Scyllo]

In your case you seem to be assuming that a corrupt GCD is the problem and often after a firmware update using GarminExpress or WebUpdater, or simply manually placing a later version GCD in the ....
This is why it's safer to update via a gupdate.gcd in a Garmin folder on a media card because if the GCD is faulty it still 'bricks' the device but then removing the card allows the device to boot.

TLDR: You must load cure firmware so you can delete suspect files progressively and as a last resort re-format.

Thank you but I currently have no problems with my device (2599LMT-D).

However, I had this once (boot loop) and was able to solve it successfully at the time using GarminCure3.

But I had not paid attention at the time whether a GUPDATE.gcd is on the device when it was in MSM mode, but have flashed the original FW (.rgn) directly afterwards.

And your statement ("There's only need to delete it, if present, before updating manually by RGN [...]") just sounded as if you always have to delete it before importing an .rgn.

Now I was worried that if the whole thing happened again, I might not even be able to load the Cure.rgn, as there might be a corrupted GUPDATE.gcd on the device itself.