Can somebody share their experience with mysterious disappearance (or re-appearance) of A/R entries? The disappearance is caused by "paid" status set by the system

I have my own experience as well, psqbo.

Once the invoice is paid, the A/R entries will no longer show. In your case, it seems like the customer has credits and it has been automatically applied to the invoice. When you turn on the Automatically apply credits feature, the available customer credits will be automatically applied to any open invoices. 

Let's check if the feature is turned on. This can be the reason why the invoices are showing as paid. Here's how:

1. Click the Gear icon.
2. Choose Account and Settings.
3. Go to the Advanced tab.
4. Click the Pencil icon in the Automation row.
5. Verify if the Automatically apply credits box is checked.

You can always get back to me if you have other questions regarding this matter. 

All the automation settings are turned off.  This behavior was not consistent. It happens randomly. If you have access to my A/R, I can give specific examples of this. In one case, after we had received payments and set to "Paid",  it put it back in our A/Rs. We followed up with customer only to realize that it was just that the system randomly decided to remove "Paid" status and removed our deposit transaction info. In other case, it removed an A/R entry by putting "Paid" status when it was not even due for payment. I suspect these are random data corruptions caused by QB updates. I can give specific invoice numbers in our system if you are available for a live screen sharing session. Thanks 

Thanks for getting back to me, psqbo.

I suggest reaching out to our QuickBooks Online Customer Care to have this investigated further. A phone agent has appropriate tools, like screen sharing, that can help you resolve this issue.

Here's how to contact them:

1. Visit our website: https://help.quickbooks.intuit.com/en_US/contact.
2. Choose QuickBooks Online.
3. On the Contact Us page, choose a topic.
4. Click the Get Phone Number button.

You can always visit us anytime if you have other concerns. We're always here to help.