The system is not stable at that time. They are rebalancing the network. It is now back to normal because they increase the 10 x resource credits.

Can someone explain how this new system works and why it makes any sense at all?

It is quite hard to explain but If you have more SP you will get more RCs. They try to stop comments and posts spammers. So they remove account createion wiht SP delegation. So no more free account can be made. No SP means no activity you can make in Steemit. In this way every users from now on has to use their money to make engagement. That may pull up Steem price. So I think this is a good change.

Currently with my SP comments I made cost only a few RCs. This is below 1% and refilled very quickly. This is good for me but they will change it later I think. They are try to stopping spammers so they will make a limitation for sure.

This is fair I think because previously no limition on comments. So spammers make comments on a lot of post. Now they can not post as they wish they have to wait or buy SP.