You opened the Plant Manager in Revit for the first time since opening Revit. It seems to be taking an excessively long time to load up, and it may be causing the program to be unresponsive during that time.
When the Plant Manager opens for the first time, it needs to load all the library family REF (.rfa) files to compare them with the existing data and prepare them for you to use. This process isn't instant, and depending on the size of your Revit plant family library, could take up to a minute. Please be patient and allow the files to load – it will save you much more time afterward once it finishes and you're able to use the planting tools.