I'd just monitor it for now. My current tank was set up in Dec of 2017 and it still is finding it's happy place. With a limited ability to add biodiversity it can take awhile for everything to get balanced. For instance, lots of stuff will eat cyanobacteria but in order for that stuff to reach a large enough population it needs to have cyano available for quite awhile. Meanwhile, other stuff is growing in your tank that will outcompete the cyano. When we interfere we can disrupt these natural cycles and can delay our tanks maturing. Some times we have to take action to save livestock or because things are horribly out of wack. This seems minor enough that I would just watch it for now.
Of course, this is just my opinion and I'm sure there are many others out there that are different than mine.