突然届き出した「感謝のメッセージ」

I use the Quizlet app to prepare flashcards for my students almost every week.

Then I suddenly started to receive these "thank-you messages" every now and then since this month.

This is a pleasant surprise as it never happened for the past several years.
They may have added a new function to this app recently.

I wonder if the Quizlet encourages my students to thank me every time they learn new words with this app.