I don't think there's a bug.

I'm in Primal too, but I DF queue only as healer, solo. The only queues that "never ended" were Coil turn 3. The rest of the Roulette's and Raids all pop within minutes. (Again, Healer.) The current longest waits are for T5, which people abandon within 10 minutes if they wipe at all.

When watching the queues when they last longer than 5 minutes, Particularly for Labyrinth, T5 and Garuda/ThornMarch Extreme, the Tank slot always jumps between 0,1,2, while the DPS slot jumps between full, or 1 short. If someone withdraws from the long queues, then it will go back to 0 on all, then after a minute you'll see the queue refill like it was before still waiting on 1 tank, 1 healer or 1 dps.

I'm thinking the estimate is based off instances actually completing. eg, that's not an estimate for how long YOU are waiting, but how long EVERYONE is waiting.