This is an itermittent bug that I've run into multiple times now, weeks apart. I can't tell you how to replicate the issue, unfortunately.
In the most recent instance of this bug, I had a screen I was designing in Builder. I had a number of data cells I wanted to rename from the default names they were given when I first placed them. I was able to change all of the names without issue, except for one named "DataCell3". I would select the problem data cell and select the name field. It would allow me to edit the name field like normal. I change the name to "Person2". As usual, once I type , the cursor disappears and the font size goes back to full size, showing that I am no longer editing the field. But then, if I de-select the data cell and re-select it, I see that the name has reverted back to "DataCell3." I tried refreshing the page, but I still was unable to change the name of that data cell without it reverting back to "DataCell3" as soon as I clicked away.
I ultimately gave up. I was able to continue using the auto-generated name, but it's certainly not ideal.