Receiving error with GmailApp.SendEmail all of a sudden

I have an Appscript program that I've used for a long time. It sends me an email with an attachment. The attachment is a Google sheet that has been exported to an xlsx format.

All of a sudden, I'm getting the error: Exception: Service unavailable: Gmail

I use this about 10 times a day, so I don't think I'm hitting any rate limits.

Here is a minimal example:

let spreadsheet = SpreadsheetApp.getActive();
let spreadsheetId = spreadsheet.getId();
let sheetName = spreadsheet.getActiveSheet().getName();

let sheetId = spreadsheet.getSheetByName(sheetName).getSheetId();
let url = `https://docs.google.com/spreadsheets/d/${spreadsheetId}/export?format=xlsx&gid=${sheetId}`;
let params = { method: "GET", headers: { "authorization": "Bearer " + ScriptApp.getOAuthToken() } };
let response = UrlFetchApp.fetch(url, params).getBlob().setName(sheetName);
let email = "myname@mydomain.com";

GmailApp.sendEmail(email, 'subject', '', {
  attachments: {
    fileName: 'filename.xlsx',
    content: response.getBytes(),
    mimeType: `application/xlsx`,
  }
});

Interestingly, it works if I remove the attachment. I tried it with different attachments and formats too and all return the same error. I also tried it in Incognito. I would really appreciate any help! Thanks!

Potential Workaround:

I encountered { [Exception: Service unavailable: Gmail] name: 'Exception' } to your code but as I've tried the solution that I created and to make this work by making the body parameter not blank or filled.

Sample Script:

  GmailApp.sendEmail(email, subject, ' ',{
      from: 'test@email.com', 
      attachments: {
        fileName: filename,
        content: response.getBytes(),
        mimeType: `application/${format}`,
      },
    });

Reference:

Class GmailApp