Got me guessing.
1. Use one of the inprivate browser windows as this contains any cookies and flushes them on exit so it might give some separation. Open Safari, from a web page bring up the base line menu with + private and done on the row, select private to get a private window - if you have not done this before.
2. Try downloading one of the other browsers to see if it performs differently.
I had noticed some of the posts getting large unread numbers recently which suggests that our glorious leader is hitting things with a hammer on the server. I usually use the "mark all read" once in a while to clear this.
Tell me what happens if you try these to.
I am using Wind10, MacOS (old version) and up to date iOS and iPadOS and not having an issue this end.