Why does a part of the details disappear when updating in the app?

It's nice to have you here in the Community, @userkadasrvcs. 

I can see that updating transactions with the mobile app is essential for your business as you can do it anytime and anywhere. It's my priority to help you modify your estimates or invoices using your device by performing some troubleshooting steps.

The behavior you've experienced can happen when there are issues with your application or mobile device. To start, make sure that your WIFI data connection is strong enough to support the process of updating the transactions. You can switch it if needed. If it is and the issue persists, you can close and restart the application.

If the issue continues, clear your app's cache to remove the historical data and access your QuickBooks account with a clean slate.

For QuickBooks Online app:

• Android 
  1. Select the menu at the top right, then choose Settings. 
  2. Click Refresh Data.
  3. Hit Yes.
• iOS 
  1. Select the menu at the top right and then choose Help & Feedback. 
  2. Tap on Refresh Data.
  3. Click Refresh.

In your Phone Settings:

• Android 
  1. From your phone's settings, select Apps (varies by device). 
  2. Choose the QuickBooks app from the list.
  3. Select Storage, then Clear Data.
• iOS 
  1.  From your phone's settings, select Settings.
  2. Click on General and choose iPhone Storage. 
  3. Select an app that's taking up a lot of space. 
  4. Tap Offload App.

Once done, try to edit your transactions to see the result. I'm also adding this link for more hints while working with the QBO app: QuickBooks Online app overview.

But if you're getting the same result, you might need to uninstall and reinstall the app.

You can always leave a comment below if you have follow-up questions while working on your transactions. I'm here to help. Keep safe!