„Wortfindungsschwierigkeiten“ would work, literally just means „word - finding - difficulties“

It’s not exclusively made for this but is actually a word that you will hear out in the wild from time to time. For a more specific word we could say something like „Okkasionalismuslosigkeit“ which would translate to „The Absence of an occasional word“, but this is probably the first and last time that is used by anyone