It is not unusual for exact 12 marker matches to disappear at higher levels, especially if they are common haplotypes (STR patterns) like the Western Atlantic Modal Haplotype, which is found in a very large number of European men. Although the FTDNA Tip reports make it look like the match is fairly close, in fact an exact 12 marker match may be many hundreds or even more than 1000 years ago. So when you go to higher levels, where FTDNA imposes more stringent matching criteria, those individuals do not show up on your match list.

It may be helpful for you to join some surname and haplogroup projects where the administrators could advise you about further testing to clarify your paternal relationships.

Jim