No replies while paid membership is on, lot of messages once the membership expires

Пришло ваше время и не думайте что оно долгое. Общайтесь и делайте выбор.

I had the same experience on the other site.  
The answer: it was randomly. Or those men/women were shy to reply you as they knew you`ll reply them back as you paid for the membership. Just a game. But very strange as such sites are for chatting/meeting/creating couples, not for running away after gettig 1 message.

P.S. These days I get more letters too. Maybe men feel March is comming...like cats 

My advise: if you got a lot of messages - use this chance. If you can reply them only after paying for the membership - do it.

That has already happened to me.
Well, as you and me are registered and active users on this site currently, we are able receive letter here. That is normal.
If you have a membership, you can opt to send a letter to anyone or not. If you send a message to someone, then there are more two possibilities: either the destinatary will reply you (before or after the expiration of your membership) or not. That will depend on the fact if the letter was read or not, how active is the user, the interest of the respective member in you, the demand of contacts, presence of fake, account settings, blocked users, and other things. So, for several reasons, including the weird or bad intentional ones, the quantity of letters sent or received per period may be varied along the time.

It also depends on how long the membership is running.
If he had a 1 month prescription , I personally believe that it is a too short period.

On the other hand , if his paid membership is for 6 months , and no one sends him a reply , you may start to wonder.

And when his prescription ends after 6 months or 1 year , and all of a sudden he is getting many letters , well , scratch your head and decide if you want to take another membership ....