EVERY WEEK: Error 401 Missing Required Authentication Credential

The title sums it up well. Every week, like clock-work I get the 401 missing authentication credential error. I have to go into Post SMTP, open the setup wizard, and reconnect my API tokens. I don’t have to change anything, I just have to go through the wizard again with the same Client ID and Client Secret. I manage a website for a client. Sometimes I’m able to catch it first myself, sometimes I get an email from my client forwarding me the error code that was sent to their email when one of their customers tried to place an order. It has been very bad for business, and I can’t find any solutions online. I have found a few forum posts from the past few weeks seeming to describe the same issue, but none of them were actually resolved.

Here is the error text that gets sent in an email:

“The log to paste when you open a support issue:
{
  “error”: {
    “code”: 401,
    “message”: “Request is missing required authentication credential. Expected OAuth 2 access token, login cookie or other valid authentication credential. See https://developers.google.com/identity/sign-in/web/devconsole-project.”,
    “errors”: [
      {
        “message”: “Login Required.”,
        “domain”: “global”,
        “reason”: “required”,
        “location”: “Authorization”,
        “locationType”: “header”
      }
    ],
    “status”: “UNAUTHENTICATED”,
    “details”: [
      {
        “@type”: “type.googleapis.com/google.rpc.ErrorInfo“,
        “reason”: “CREDENTIALS_MISSING”,
        “domain”: “googleapis.com“,
        “metadata”: {
          “method”: “caribou.api.proto.MailboxService.SendMessage”,
          “service”: “gmail.googleapis.com“
        }
      }
    ]
  }
}”