Here are a couple of reasons why your WorkFlowy account may be slower than usual in loading... and a couple of possible solutions:
Having more than one browser tab open at any given time will cause an increase in loading time, since one tab alone consumes significant resources. Basically you're loading the same number of unique URLs as the number of bullets you have. So if you have 100,000 bullets in your account, WorkFlowy loads 100,000 unique URLs upon startup.
Here are 2 possible solutions:
1. Keep just one tab open and use the 3rd-party WFx extension, which allows you to jump from one list to another with your own shortcuts. In fact, this is quicker than changing over to a different WorkFlowy tab. Here's the playlist to a series of screencasts on the extension:
You should watch #4 in the list (List Jumping).
2. If you were to export some of your project outlines that you don't need access to (to, say, Dropbox), you could dramatically decrease load times all 'round. I'd recommend exporting via all 4 file options currently available and bundling those into one folder per project.
Whenever you want to import exported outlines, the best method would be to copy the content of any exported OPML file and paste it into WorkFlowy.