Calendar DeltaQuerys always result in HTTP 503 or 504 error response

Question

I am using a custom application that uses the Microsoft Graph REST interface. Through this REST interface I regularly request changed dates using DeltaQuerys.

I have the problem that with some users, the DeltaQuery REST requests always result in an HTTP 503 or 504 error response. This does not change even if the queries are repeated after waiting for some time or even in the next few days. The error also occurs if the DeltaQuery query is executed without DeltaToken or SkipToken, it then comes back on the same result page.

Changed appointments can only be queried again after certain mostly daily long-running appointment series with many exception appointments has been deleted. I do not know what to change in the query. There is no way to tell which appointment series are causing the problem and need to be deleted.

The last query with this error was this one:

2021-03-23 13:42:03,391 Request: GET https://graph.microsoft.com/v1.0/Users('...')/calendarview/delta?%24skipToken=aVxnGmD_iauljNDUWJs5WrXLyr_lwnfNiDvP-lcTAFa_UvBvr8wWslITny9WhaMfWACh0-OAnbh3WthBwHwGzHhAIo5vQfyuzaNTzlG4YdIcistSWcGnd_k4woip1k6Lm7IaHAJSYKzh0Sv5R6nBLUNTldsS_Pf7n2yvldImrFNYctGchB7319D8wCbG7MJTp3frgANJ0IesjZemQQq2UYb1x8ZJj7ch9r1SxTURZY3c-yFftH93NMwXTPyjuk0d.DjcXPsqmTgRw_0ygOoRjf891oiOX87OU4iOLpFD_eoc

Response: HTTP 503 (duration: 23907ms)

{   
  "error": {
    "code": "UnknownError",
    "message": "",
    "innerError": {
      "date": "2021-03-23T12:42:03",
      "request-id": "64b1743b-69c4-4602-a282-fd632f256e02",
      "client-request-id": "4f7f37be-ad58-4f75-bc70-16228360b5eb"
    } 
  }
}

With kind regards, Demian