I only have one open forum tab on one browser on one computer so unless someone is hacking my account somewhere else .......
Just a glitch. I see it occasionally if I've half done a post then moved to another thread to edit (or some other conditions Just refresh & it goes away.
But if you are worried, change password. Might even be 2 factor authentication available (I haven't checked)
I don't think its a hacker
I'll go with glitch in The Matrix