It's not declined, I am currently checking this. The only correct solution is to increase the amount of mission rooms until this doesn't happen anymore.
I can understand though that having activity points wasted is a real bad feeling.
What I must say though is that people should stop complaining and asking for refunds AFTER they have tried to enter 3/4/5/x times.
If you try to enter once and it fails you know something is wrong. We can't refund activity points or solve this problem without a maintenance.
I've tried and got nothing for 7 tries today and 6 times yesterday.
I'm not asking for a refund, but I am complaining because this happens often, and you can't really expect people to not try multiple times to get entry to their ranked missions given the fact that using up lots of AP potions usually happens when there is a 1 vis event so its expected that they would want to just do their ranked missions before the event ends.
Also this usually happens only on UD/LL and weekends, so I suggest to just make it a free-for-all 7 days a week, that way the server wont get congested with people trying to spam within those days. That would make everything better, it also benefits those who just want to do rank to finish some quests, because if you miss out on a day, you'd need to wait 3-4 days to get that racial rotation again.