Logic conditional greyed out

Hi

we have a a group of fields ACF with 2 fields, one is a file type field
A lot of posts use this field, but on some posts this field is not used
So I enabled logic conditional to hide this field when the field is empty, but when I enable this functionality I can’t select the 2 entries in the first field, why ? they are greyed out !!

I tested on another field and it works… but on this one not
what i can do?
thanks