What does ExtensionError: Operation: Create; Exception: [A task was canceled.] mean?

Question

I am attempting to create a subscription to Outlook messages for a user.

{
	"resource": "/users/<userid>/messages",
	"change_type": "created,updated"
}

The Graph API responds with a 500 error.

{
	"code": "ExtensionError",
	"message": "Operation: Create; Exception: [A task was canceled.]",
	"innererror": {
		"client-request-id": "1ecf5f0f-9d6e-4ba0-86d1-8890f42508f2",
		"date": "2023-09-14T16:45:09",
		"request-id": "1ecf5f0f-9d6e-4ba0-86d1-8890f42508f2"
	}
}

This typically works without any issues. I have recently begun seeing this error sometimes. I am getting it every time for at least one specific user_id.

Here is a list of headers from a request:

Cache-Control:[no-cache]
Client-Request-Id:[1ecf5f0f-9d6e-4ba0-86d1-8890f42508f2]
Content-Type:[application/json]
Date:[Thu, 14 Sep 2023 16:45:09 GMT]
Request-Id:[1ecf5f0f-9d6e-4ba0-86d1-8890f42508f2]
Strict-Transport-Security:[max-age=31536000]
Vary:[Accept-Encoding]
X-Ms-Ags-Diagnostic:[{
	"ServerInfo": {
		"DataCenter": "West US 2",
		"Slice": "E",
		"Ring": "1",
		"ScaleUnit": "004",
		"RoleInstance": "MW2PEPF0000E062"
	}
}]

What does Operation: Create; Exception: [A task was canceled.] mean?