Great. Please inform the developer mailinglists of GNU nettle and GnuTLSabout the regression(s).
I will post about the segfault problem in GnuTLS 3.6.0 on the GnuTLS list.
Regarding the dowgrade from 3.5.15 to 3.3.26, I really do not know wheter the problem is with the newer GnuTLS or the way microhttpd uses it.
As for nettle, I have no reason to belive either version has a bug, but GnuTLS 3.3.26 required 2.7.1.
Best regards, Svein Olav Bjerkeset