No response from bot

Hi. We got somewhere around 50 users talked to the bot on Facebook. It was not simultaneously but during 24 hours starting from early morning. Somewhere after lunch time iVan stopped reacting instantly and got frozen for a good amount of time. In my personal case it did not reply for several minutes. Then he woke up and sent the same messages all at once. Here is one of such cases when iVan replied only after 2 minutes after the user's input - screenshot attached.