VANISHED not working with cyrus proxy

[alecpl]

We're using Cyrus Murder 3.6.3 setup. Here's the error:

[10-Jan-2024 12:29:19.352378]: C: A0214 SELECT Test
[10-Jan-2024 12:29:19.399869]: S: * OK [CLOSED] Ok
[10-Jan-2024 12:29:19.400106]: S: * 1 EXISTS
[10-Jan-2024 12:29:19.400235]: S: * 1 RECENT
[10-Jan-2024 12:29:19.400332]: S: * FLAGS (\Answered \Flagged \Draft \Deleted \Seen)
[10-Jan-2024 12:29:19.400435]: S: * OK [PERMANENTFLAGS (\Answered \Flagged \Draft \Deleted \Seen \*)] Ok
[10-Jan-2024 12:29:19.400531]: S: * OK [UNSEEN 1] Ok
[10-Jan-2024 12:29:19.400628]: S: * OK [UIDVALIDITY 1577540428] Ok
[10-Jan-2024 12:29:19.400721]: S: * OK [UIDNEXT 2] Ok
[10-Jan-2024 12:29:19.400813]: S: * OK [HIGHESTMODSEQ 53] Ok
[10-Jan-2024 12:29:19.400906]: S: * OK [MAILBOXID (e7534bd5-198d-42a9-822d-e5adb478b933)] Ok
[10-Jan-2024 12:29:19.400998]: S: * OK [URLMECH INTERNAL] Ok
[10-Jan-2024 12:29:19.401090]: S: * OK [ANNOTATIONS 65536] Ok
[10-Jan-2024 12:29:19.401183]: S: A0214 OK [READ-WRITE] Completed
[10-Jan-2024 12:29:19.417594]: C: A0215 ENABLE QRESYNC
[10-Jan-2024 12:29:19.459301]: S: * ENABLED CONDSTORE QRESYNC
[10-Jan-2024 12:29:19.459683]: S: A0215 OK Completed
[10-Jan-2024 12:29:19.459931]: C: A0216 UID FETCH 1:* (FLAGS) (CHANGEDSINCE 52 VANISHED)
[10-Jan-2024 12:29:19.505736]: S: A0216 BAD Invalid UID Fetch modifier VANISHED

It does work when connecting to the backend directly.