As some of you might have noticed the tor network recently lost a noticeable number of relays and bridges as seen in the metrics.tpo relay graphs (0.7% cw fraction).
https://metrics.torproject.org/networksize.html https://pbs.twimg.com/media/DwGAESoXgAEoB6L.jpg
this occurred when these relays upgraded from tor 0.3.3.10 to 0.3.4.9 (package maintainer update)
All these relays were behind NAT devices and they relied on a tor feature that got removed between these two versions:
o Removed features: - The PortForwarding and PortForwardingHelper features have been removed. [...]https://trac.torproject.org/projects/tor/ticket/25409
The portforwarding worked only in about 5% of cases so only 350 of the over 6000 relays actually became reachable.
Since I still believe these relays are not run by humans I hope they remain unreachable behind their NAT routers.