Period came back on IUD?

I got my IUD about 4 years ago, I have another year left before I need to get it taken out or replaced. I stopped having periods probably within 6 months after getting it inserted. I do have some light spotting occasionally, maybe every couple months, but that's it. I wouldn't even consider this a period, it only lasts a day or two and I don't typically have to use any period products. Last month, I started bleeding very lightly, nowhere near what a normal period used to be but enough I needed to use a liner for four or five days. I did take a pregnancy test after this as a precaution and it was negative. It's been about a month and I'm having the same amount of bleeding, I'm assuming this is my period coming back. Has anyone else had this happen? Is this cause for concern? I've tried to search on this but didn't come up with much.