I hope you're enjoying this Tuesday morning so far.
I recommend clearing the web browser's cache. Web browsers collect cache (cookies) to save you time when loading repetitive data and images. These files can often become outdated or corrupted, causing issues like the one with your categories missing. Clearing them out usually resolves these issues. Below I've included links for all supported browsers that include steps for clearing cache.
Once you've cleared the cache, close your web browser and restart it. Sign back into QuickBooks Online to see a fresh copy of the data.
Please don't hesitate to let me know if you have further questions or concerns. I'll be here to help you every step of the way. You can always reach out to the Community or me anytime you find you need assistance. Take care and have the best week ahead. You deserve it!