It wasn't a bug because I contacted admin myself when my profile's activity was frozen, he said the activity freeze is natural during ranking and it will be unfreeze if certain requirements are met. I believe the admin has changed some code on the forum and now we may not see that activity freeze anymore, however we need to hear from the admin first.
It's not a bug, it's a feature of the forum. And I don't think this feature is going to be eliminated (although it could be modified by the administrator if he has a new idea to implement) since, although it may not seem like it, it prevents some users from writing large amounts of meaningless posts with the intention of increasing the ranking of their accounts, and it also means that the user must spend more time connected to the forum, posting at a slower speed, always looking for a balance.
It is very much possible. I don't know if you have an account on the Bitcointalk forum or not. But I have seen the campaign manager doing this. For example, you are in the Mixero campaign and the manager is Royse. He runs the same campaign on BitcoinTalk and this campaign has bigger payments for users who have more than three thousand merits. If I remember correctly, the users with more than 3000 merits were getting $5 per post which is incredible. Currenctly, the campaign pays 1.2 USD because the forum does not have activity like Bitcointalk. Managers may increase the pay rate as the forum grows and I am sure that the Karma and the rank will be considered as fact in the future.
It is normal that the payments here are quite low, due to the traffic as you already know. But if the forum continues to grow (even little by little) we will surely have more campaigns with better payments and greater "rivalry", something that is always good, for products and brands and also for users. But maybe it's too early to talk about it, now we should continue contributing everything we can.