1. Open the /_admin interface of an installed surfer app
2. Select index.html (or any file)
3. Click on 'Download'

Expected result:
File downloads

Actual result:
Screen shows: This app is currently not responding. Please try refreshing the page in a few minutes.

In the logs I see this error:

Jun 05 04:38:24 get: /app/data/public
Jun 05 04:38:44 2026-06-05T03:38:44Z 
Jun 05 04:38:44 2026-06-05T03:38:44Z 
Jun 05 04:38:44     at FSReqCallback.oncomplete (node:fs:199:5)
Jun 05 04:38:44     at SendStream.emit (node:events:518:28)
Jun 05 04:38:44 Node.js v22.14.0
Jun 05 04:38:44 TypeError: contentDisposition is not a function
Jun 05 04:38:44 ^
Jun 05 04:38:44 at SendStream.send (/app/code/node_modules/send/index.js:508:8)
Jun 05 04:38:44 at SendStream.setHeader (/app/code/node_modules/send/index.js:739:8)
Jun 05 04:38:44 at SendStream.setServMiddlewareHeaders (file:///app/code/server.js:58:75)
Jun 05 04:38:44 at onstat (/app/code/node_modules/send/index.js:615:10)
Jun 05 04:38:44 file:///app/code/server.js:58
Jun 05 04:38:44 if ('download' in res.req.query) res.setHeader('Content-Disposition', contentDisposition(path));
Jun 05 04:38:45 2026-06-05T03:38:45Z 
Jun 05 04:38:45 => Ensure permissions
Jun 05 04:38:45 => Start the server
Jun 05 04:38:45 Base path: /app/data/public
Jun 05 04:38:45 Config file /app/data/.surfer.json not found
Jun 05 04:38:45 Listening on http://localhost:3000
Jun 05 04:38:45 Loading rich mime-types from /usr/share/mime/globs2
Jun 05 04:38:45 Using config file at: /app/data/.surfer.json
Jun 05 04:38:45 Using tokenstore file at: /app/data/tokens.json
Jun 05 04:38:45 Warning: connect.session() MemoryStore is not
Jun 05 04:38:45 designed for a production environment, as it will leak
Jun 05 04:38:45 memory, and will not scale past a single process.

Additional information:

• I tried to restart the app many times
• I recently restored the app from a backup
• the app version is on Surfer 6.6.1. Same behaviour was on 6.6.0
• Downloading the file from the Files Manager works seamlessly

Additional wish: is it possible that releases contain some hint on what changed in a package update? The latest update 6.6.1 didn't contain information. Neither on Github nor directly in the notes. I also checked the notes in https://git.cloudron.io/packages/surfer-app. I found changelog which was maintained until 9.4.7