I hope your day is going well so far. Once you made the changes on the customer page, did you click the save button at the bottom right-hand side? Below is a visual.
If so, then I recommend clearing your browsing data. After history has been stored over some time in your browser, it can cause error messages or even glitches within different softwares. Here's how to clear your history in Google Chrome:
Go to the Three Vertical Dots in the top right-hand corner.
Choose History and then History again.
Hit Clear Browsing Data.
Select All Time in the "Time Range" section.
Press Clear Data.
Afterward, log back into your QuickBooks account and see if the changes saved.
I want to make sure that you're able to get this resolved, so let me know if this helps. Have a great Thursday!