I ran into various issues with AutoNAT in May this year (3889, #3986 and #3900), both with TCP and QUIC. These problems are supposed to be solved with a new AutoNAT version. For the implementation of AutoNATv2, there are some features that have to be implemented first.
Yesterday I noticed there is a developer that got a grant from Filecoin to work on AutoNAT version 2:
AutoNAT being about detecting NAT status, it’s the first step, and without this first step working properly we can’t do NAT traversal yet. The second step (relays) should work. The third step (hole punching/DCUtR) should work with TCP and was implemented for QUIC in June (#3964).