I'm here to ensure you can easily categorize transactions in QuickBooks Online, @kathy42. 

Let me discuss some ideas and tips to rule this out.

I tried to categorize transactions in bulk using the same steps you perform, and everything seemed to work fine. 

Transactions will not hold or go back to their original category if you Undo them. If you didn't undo the transactions and still get the same result, then you're likely experiencing a browser-related issue. 

I recommend performing some basic troubleshooting procedures to isolate the problem. Start by signing in to your QBO account using an incognito page. Here are the shortcut keys to open it:e

• For Firefox or Microsoft Edge, press Ctrl + Shift + P.
• For Chrome, press Ctrl + Shift + N.
• For Safari, hold down Command + Shift + N.

If you can categorize the transactions properly, you'll have to clear your regular browser cache. This prevents unusual browser behavior. 

If the issue continues, use another supported browser.

Once you're all set, feel free to read this additional module about matching your account and bank statements: Reconcile an account in QuickBooks Online.

Fill me in for more help about banking or QuickBooks. I'm always ready to assist. Take the best care!