Suddenly can't upload custom Token Markers

Yesterday, I made some custom sets for Token Markers, and today I can't upload images to any of my sets or new ones. I can normally upload assets to my campaings and I still have free space, but still this doesn't work only for Token Markers. Restarting or changing browsers doesn't fix the problem and all I'm getting is this.

My storage says I have 2-3 MBs I might have deleted a couple art assets in the last day or two, but I think it was before I made the first Markers that actually worked. I also have checked, and apparently the Markers work now. I have had some problems in the past where deleted assets didn't free up the storage and it didn't update for a bit, so it might've been that (but also the display did update when the storage actually got freed up, and it took about 5-10 minutes, while here I tried every couple hours while display still said I have free space).