samsung S8 note 8 A8+ and other looses basenband

hello support and mates .. have you come acroos with this cases lattely
i have come across with next models
n950f
a730f
g950
g955f

that after you rebrand o put another firmware from other carrier it loosed baseband , is there any fix for that?

all happends the sameafter upgrade to android 9
if you downgrade to android 8 (when is possible) baseband comes back