Where was the Roman Army in AD408?

[Nathan Ross]

at this time the Palace guard seems to have been commanded by the Cura Palatii, not the Comes Domesticorum

At which time? There's no cura palatii in the ND, and Zosimus's account of the events of 408-10 seems to to support the Comes D as the most important bodyguard commander - what's the earliest date you have for the 'cura palatii' as a guard commander?

The Candidati were the 40 personal guards of the Emperor, and were part of the Scholae.

Which would surely put them under the command of the magister officiorum, who was in charge of the scholae after 395?

Could Comes Domesticorum and Cura Palatii have become the same title?

Unlikely, I think. I'd never heard of the cura palatii, but it sounds like it would originally have been a civilian role, similar to the castrensis sacri palatii ('marshall of the sacred household') perhaps. Is your source a much later one which uses anachronistic terminology, perhaps?