I have exactly this same problem. I thought it might be a memory problem or something. I recently got a brand new computer and clean installed everything, and I still have this issue. It is a huge efficiency issue. Every workbook has to be constantly max/min'd to get the worksheets usable. I need a fix. (I have attempted to disable everything else, and it doesn't make a difference.) If I disable KuTools, the problem goes away. I'm also using Office 365, 64-bit, Kutools 18.