Connection issue when backlog quota is exceeded - unable to consume

[devinbost]

It seems that there's an edge case that's not handled properly when a backlog quota is exceeded.
The clients aren't able to connect, and I understand that they shouldn't be able to produce, but consumption gets blocked as well, even if the downstream topic has no subscribers (so the messages should be easily consumed, thus resolving the backlog.)

[codelipenghui]

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