Photoshop Brush Sizes Not Working Properly

I am having this problem where I size up my brush, but about halfway through the brush size preview starts to get smaller again, except this middle part which stays about the same size and is faded in the background. The actual brush itself gets smaller too, I cannot get it to be bigger than 150px or so. I would like it so I can make my brush size bigger to the fill 3,000 px size. I've attached a screenshot which shows this too. I don't think this is normal and I know it sounds weird, but if any of you know a fix to the problem, I would appreciate that very much. I have a 2012 Mac Mini running MacOS Sierra with Photoshop CC 2017. Let me know if you still need any clarifications.