Mr. Florin Curta tells me it seems for him as slavic
specialisttoo, very strange that the gepides fought the slavs
and this in the sec VII.
He quoted as fallow:

Procopius in "The wars VIII 25.1-6) said the roman army were
not able to do anything in 551 AC when the slavs devasted the
nord balcanic provincias where the sclavinis crossed the
Danube and they got help from gepides. The gepides asked the
sclavinis to give them one solidus per gepidic warrior for the
services which the gepides given to slavs.

It remains for me to clear why the L. Schimdt in his "
Geschichte der deutschen Stämme bis zum Ausgang der
Völkerwanderung.Dei Ostgermanen" makes the same mention as Muh
Sun Lee.I did not read this book so I cannot say anything
about this..