I'm not totally familiar with the implementation here, so pardon if this is a naive question. The other two sends call increment_received_event_count_and_byte_size before sending, this one never calls it. Is that an omission?

Sorry for that, My previous commit did indeed contain an error. I've never used Overflow before, and after my build is tested, I've forgot the last case of WhenFull::Overflow, apologize.
Because resolving this issue requires updating the counter before sending the event to the buffer, when handling the Overflow branch—if the overflow logic is triggered and the message is sent to overflow buffer—the counter needs to be decremented. However, neither using send nor drop to perform this countdown is quite appropriate. Therefore, to address the problem I was facing, I chose to ignore this particular scenario for temporarily.
Now that I think about it again, maybe using drop to update the counter is actually reasonable—since the event is effectively "dropped" into the overflow buffer?
I've updated my commit, but not tested.