New Outlook: This message can't be saved right now. Please try again

We are having an issue in New Outlook with shared mailboxes.   This issue just started happening.

User replies to an email in a shared mailbox.  User changes the "from" field to her email.  User tries to send the email but receives an alert "This message can't be saved right now.  Please try again later."

The message then closes and a copy of the email is saved to the Drafts folder.

No permissions have changed.

If user tries the same actions in the Outlook Web Client or Classic Outlook, the user is able to send the email without issue.

We've tried resetting New Outlook, restarting Windows, behavior persists.

Again, this function was working up until recently.

Microsoft Outlook Version: 1.2026.317.100

WebView2 Version: 146.0.3856.84 (Stable)

Please advise how we can resolve this issue.