Roman army units in the Post Roman West

[Robert Vermaat]

As far as I know, Stilicho took away most Roman forces, and I do not exclude the possibility that Procopius presented Frankish units as Romans.

Not so.
Not only does arcaeology by no means attest that the forts were deserted, but what we can read from the Notitia Dignitatum also by no means suggests that Stilicho did anything like that. The Rhine was not deserted, not were other troops in Gaul or Britain taken away on such a scale.
It was the magister militum per Gallias Aegidius who in 461 rebelled with his forces, who no doubt were very Roman troops. After the Toxandrian Frankish king Clovis beat Aegidius' successor in 486, the latters' Roman army (exercitum Romanorum) was incorporated into Clovis' Frankish army (exercitus Francorum).