I asked to ChatGPT 5.0:

I’m on Cloudron trying to Update Vikunja app to 2.5.0 , but I get this error:

level=ERROR msg="Migration failed: migration 20260720120000 failed: cannot recreate the unique index on tasks (project_id, index) because 2 sets of duplicate values exist — remove the duplicates manually, then restart Vikunja"

what I’ve to do?

Then ChatGPT answered with MySql different queries, then I told:

I’m on postgres

Then gave me this answer:

For PostgreSQL, follow the same principle: keep one task in each duplicate set and assign new task indexes to the others.

1. Back up Vikunja

Create a manual Cloudron backup before modifying the database. Ideally stop Vikunja or ensure nobody is using it during the repair.

2. Connect to PostgreSQL

Open the Vikunja app’s Terminal and run:

psql "$CLOUDRON_POSTGRESQL_URL"

If that variable is unavailable:

PGPASSWORD="$CLOUDRON_POSTGRESQL_PASSWORD" psql \
  -h "$CLOUDRON_POSTGRESQL_HOST" \
  -p "$CLOUDRON_POSTGRESQL_PORT" \
  -U "$CLOUDRON_POSTGRESQL_USERNAME" \
  -d "$CLOUDRON_POSTGRESQL_DATABASE"

3. Inspect the duplicates

SELECT
    project_id,
    "index",
    COUNT(*) AS count,
    ARRAY_AGG(id ORDER BY id) AS task_ids
FROM tasks
GROUP BY project_id, "index"
HAVING COUNT(*) > 1
ORDER BY project_id, "index";

To also see task titles:

SELECT
    t.id,
    t.project_id,
    t."index",
    t.title
FROM tasks AS t
JOIN (
    SELECT project_id, "index"
    FROM tasks
    GROUP BY project_id, "index"
    HAVING COUNT(*) > 1
) AS d
  ON d.project_id = t.project_id
 AND d."index" = t."index"
ORDER BY t.project_id, t."index", t.id;

4. Automatically reassign the extra indexes

The following keeps the lowest task ID in each duplicate set unchanged and assigns unused indexes to the others:

BEGIN;

LOCK TABLE tasks IN ACCESS EXCLUSIVE MODE;

WITH ranked AS (
    SELECT
        id,
        project_id,
        "index",
        ROW_NUMBER() OVER (
            PARTITION BY project_id, "index"
            ORDER BY id
        ) AS duplicate_number
    FROM tasks
),
to_fix AS (
    SELECT
        id,
        project_id,
        ROW_NUMBER() OVER (
            PARTITION BY project_id
            ORDER BY "index", id
        ) AS new_offset
    FROM ranked
    WHERE duplicate_number > 1
),
project_max AS (
    SELECT
        project_id,
        COALESCE(MAX("index"), 0) AS max_index
    FROM tasks
    GROUP BY project_id
)
UPDATE tasks AS t
SET "index" = pm.max_index + f.new_offset
FROM to_fix AS f
JOIN project_max AS pm
  ON pm.project_id = f.project_id
WHERE t.id = f.id
RETURNING t.id, t.project_id, t."index", t.title;

COMMIT;

This does not delete tasks. It only changes the duplicate per-project task numbers.

5. Confirm the problem is fixed

SELECT project_id, "index", COUNT(*)
FROM tasks
GROUP BY project_id, "index"
HAVING COUNT(*) > 1;

It should return:

(0 rows)

Exit PostgreSQL:

\q

Then restart Vikunja and retry the Cloudron update to 2.5.0.

ChatGPT forgot to remember me to enble recovery mode because app was unreachable at moment, but I solved.

Thanks @humpty for your patience taking look into the problem.

Do you mean browser cache?

Cloudron app does not start after update...