I noticed it based on Pi-Hole [0] and seeing the excessive DNS Requests to those URLs... started googling and found this post which I thought summed it all up nicely. Looking at the author's post, it also appears they noticed it due to Pi-Hole as well.

EDIT: It was a different post that someone had seen this via Pi-Hole. Not sure how the original author discovered it.

[0] https://pi-hole.net/