Issue Summary

Calendar Power-Up and Calendar view on the Trello iOS app (v2026.12.1) fail to display cards with due dates. The calendar is not filtering cards when dates are selected. Diagnostic logs show HTTP 401 (Unauthorised) errors on API batch requests. The issue does not occur on the web or desktop — iOS only.

Steps to Reproduce

1. Open Trello iOS app (v2026.12.1)
2. Navigate to a board that contains cards with due dates
3. Open the Calendar Power-Up view (or Calendar view)
4. Attempt to filter/view cards by selecting dates
5. Dates with cards (indicated by a dot below the date) display cards correctly when tapped. However, dates without cards are completely unresponsive — tapping them does nothing. Additionally, filtering to show zero cards (e.g., selecting a date range with no due dates) does not work as expected.

Expected Results

Calendar view displays all cards with due dates on their respective dates, consistent with the web and desktop experience.

Actual Results

Calendar view appears, but nothing happens when a date is selected. No cards are rendered on the calendar despite due dates being set. The app returns HTTP 401 errors when attempting to fetch calendar data.

The below exception is found in the diagnostic report (report.json):
 

{
  "metadata": {
    "appVersion": "2026.12.1 (20260610.210453)",
    "deviceModel": "iPhone15,2",
    "osVersion": "26.5",
    "title": "Networking Error"
  },
  "payload": {
    "errorText": "Domain: com.trello.error.trelloapi\nCode: -12\nDescription: The server responded with an HTTP error code. statusCode: 401\nUserInfo: [\"NSLocalizedDescription\": \"The server responded with an HTTP error code. statusCode: 401\"]",
    "response": {
      "statusCode": 401,
      "headers": {
        "Set-Cookie": "loggedIn=; Domain=trello.com; Path=/; Expires=Thu, 01 Jan 1970 00:00:00 GMT; Secure; SameSite=Lax"
      },
      "urlString": "https://trello.com/1/batch"
    }
  }
} 

Workaround

Use the Trello web version or desktop app to access the Calendar view. Calendar Power-Up functions correctly on both platforms.