MacBook Air removed from account while using it?

I have a Macbook Air, an iPad Pro and an iPhone. Until today all three worked normally and showed up on my account in settings. Earlier today I started messenger on my Macbook, but it asked me to enter my account details. I did that and it logged in. Then I got notifications on my iPhone and iPad that a new device was just added to my account. The thing is that when I started messenger I was using my Macbook as normal and there weren't any alerts that it was removed from my account. Surely if it wasn't on my account I couldn't use it, so now I'm confused as to what exactly happened. Any help appreciated!