I have observed online TurboTax do strange things. When data is transmitted, sometimes things just don't go through correctly.
Cancel your amend, sign out of TurboTax, then use the Chrome browser and clear cache and cookies.
Attempt the amend again. If these strange things are still happening, then contact the helpdesk for assistance.
Turbotax has been fiddling with returns that showed Unemployment tax.
For that reason you have to be super careful that your Column A and Column C on 1040-X are correct.
If you used TurboTax Online, I suggest you get 1040-X form from IRS and fill it out yourself.
"When data is transmitted, sometimes things just don't go through correctly"
what does this have to do with amending.?
Since e-File is an electronic transmission over Internet protocol, what you are claiming just should not be possible.
If Turbotax sends a bad file, the error comes earlier. IRS needs better error checking.
I have observed a person starting a return and TurboTax putting in numbers that should not be there. It is not common, but does happen. This person started an amend and had a $5000 error as soon as the amend opened. I blame a bad data transmission for that, rather than an across the board bug or an IRS error.