I was able to fill in the address of a foreign bank on Form 8938 in TurboTax Desktop without issue.
Since you're using TurboTax Online, you may have some data hung.
Delete Form 8938, close TurboTax, clear your Cache and Cookies, re-open TurboTax and go through the interview questions again to re-create Form 8938.
You could try using a different browser, and make sure you don't have any other programs running in the background (like Email) while using TurboTax.
If you decide you want to transfer your return from TurboTax Online to TurboTax Desktop (where you have access to the forms), here's How to Transfer from TurboTax Online to TurboTax Desktop.
@JimPueblo
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