This has happened to me in the past, but it's just happened again.

Trying to get into Aurum Vale as Ninja and the Duty Finder pops, I click commence as does the other DPS, healer, but not the tank. Timer runs to zero and it re groups me again with another party. Again on the checklist it showed the tank as not clicking commence, timer ran to zero, but this time it kicked me from the duty finder, so I queued again.

The same thing happened with the tank another two times, so I tried to queue again and it says that I've been penalised for 30 mins due to abandoning a duty

I definitely clicked commence on every time as it popped immediately.