My streaming service bill has a random extra charge every third Thursday

I spotted this weird charge on my statement last month and it's been happening for a while. It's always exactly $4.99 and it pops up every third Thursday like clockwork. I called their customer service and they called it a system glitch but couldn't say why it's so regular. Now I have to go through the hassle of disputing it each time, which is a pain. I've been keeping a log and it's happened six months in a row. The last rep I talked to was just as baffled as I am about the pattern. It's like their billing software has a weird calendar bug or something. Just wanted to share this odd billing quirk I'm dealing with.