Tor Browser has two default bridges that share a fingerprint, and Tor ignores one
default_bridge.obfs4.13 has an ipv4 address and identity fingerprint C5B7CD6946FF10C5B3E89691A7D3F2C122D2117C, whereas default_bridge.obfs.14 has an ipv6 address and the same identity fingerprint C5B7CD6946FF10C5B3E89691A7D3F2C122D2117C.
One might think that Tor will then try both of these addresses and if only one works, it will use that one. But that is not so, because of Tor bug tpo/core/tor#40193.
I'm not sure what the best fix is from the Tor Browser side. The easy pick would be "we should remove one of those bridge lines for now, because we're clearly not getting the redundancy we hoped for." Maybe there are better plans than that, depending on when/whether/how the network team plans to address the tor-side bug.
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