Boost for Lemmy

Since I started using Boost years ago, I've noticed that private message notifications don't really seem to clear, even after reading and responding to the message. They eventually go away after maybe a month or so but during that time it still reads that I have an unread message. I can't find any way to manually clear them that seems to stick. Mark All As Read does nothing.

Is this a bug or am I missing something?

I'm using Boost for Lemmy on Android (Pixel phone)

Edit: Mark All As Read is the double checkmark button. It doesn't always work.