Posts showing unread once read

Just mentioning that this happened to me today, just now.
Latest 2 topics I had not read. I read them and they still have a blue symbol there as of i didn’t read them.
One was solved by liking a post the other still shows as not read.
I’m connected to the net, so not sure why this is hsppening.

After creating this post it then showed as read, no big issue, just thought I would mention it.