How do you add or remove queue members? Are you talking about adding queue members or login in or out agents ?
Seems like there is a missing event in AMI or something like that, unfortunately there is no way to fix state inconsistencies if they are because of a missing event. If that happens just sometimes and you are not able to reproduce the issue, it is next to impossible to fix it.
You can paste the actual output from "queues show" on the cli so I can have a better idea....
Ah.. just came to me, if you monitor more than one asterisk server and in the server you have the same queue defined, states will be off as fop2 will receive contradictory events from servers (maybe one agent is logged on server one and not on server two)... as fop2 treats the servers as a whole..