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I have one point which is more than a nit, but not really an issue:

For some transport protocols transient numeric identifiers are covered
by encryption (like in the QUIC case), sometimes they are not (like in
the TCP case), sometimes it depends on the lower layer (like in the
SCTP/IP versus SCTP/DTLS/UDP case). The introduction discusses that
just encrypting the transient numeric identifiers does not solve all
issues.
Readers might focus on Section 5 and do not read the whole document.
Therefore, it would be good, if Section 5 would also mention, that
considerations for transient numeric identifiers have to be made even
in the case where the transient numeric identifiers are protected
by encryption.