I have noticed that if a GEDCOM contains a death date of "before …." and an otherwise identical existing profile has a blank death date with the "uncertain but non-living" box selected then the profile does not appear as a suggested match. Since death dates are one of the harder things to find, I think it would be better if a mismatch between an entered death date in a GEDCOM and a blank death date in a profile was ignored.
I have noticed this a few times, but most recently when my GEDCOM contained data for Edith Maryon Queenie Gorring, born 24 May 1899, died before 1999. I had actually already created a profile for her a few weeks ago (Gorring-6), the only difference being that I left the death date blank and ticked the "uncertain but non-living" box, but there were no suggested matches. I happened to know that I had already created her profile as I keep a note of the ones I have completed, but if the GEDCOM had belonged to a new user then they would almost certainly have created a duplicate profile.
In this case since both the name and date of birth matched precisely I think this should have been shown as a suggested match.