We are seeing across our various report suites a large delta between total visits and the number of visits that have a referrer type associated with them. Based on the Adobe definition of this dimension I would assume every visit would have a referrer type as the "Typed/Bookmarked" type is intended as a catch all for any visit where adobe does not have any referrer information for it. The deltas we are seeing range from 20% of visits all the way up to 50% of all visits depending on the report suite we are looking at.
Is this common? Is there a particular reason a visit may not have any value here?
Are you by any chance tracking Mobile App data as well? Mobile Apps do not set Referral Data (not typed/bookmarked, not anything), there is literally no "referral instance" triggered.
Check you "Internal URL Filters". It should only contain the domains that are internal to your site (with some exceptions such as payment gateways or partner pages).
"Typed//Bookmarked" is not a catch all. It is a label to show when s.referrer value was blank
A workaround that I do for these instances is through the external tracking codes, then I custom a segment, and consolidate external tracking codes together especially if there are channels aside from usual sources that you are expecting.