Single appdata JS file (merged-template-prepend.js) served extremely slowly – ~5s via curl, ~20s in browser

[BenPace-Planet]

Environment

• Nextcloud AIO, Nextcloud 32.0.8.2
• Debian 12 VM, reverse proxy mode (external Caddy in front, APACHE_PORT=11000)
• Problem started after a VM restore (only the Nextcloud VM was rolled back)

Symptom
The web UI is sluggish, most noticeable when switching apps (Dashboard, Files, Talk).
Navigation within an app is fast.

Browser network tab when loading the dashboard shows exactly one slow request:
merged-template-prepend.js -> 20.67 s (initiator: dashboard:40)
All other ~146 requests complete in 190-640 ms.
The Web Inspector shows this request's bar as solid green (content download).

Measured locally on the VM against the AIO apache container:
curl -s -o /dev/null -w "Time:%{time_total}s\n"
"http://127.0.0.1:11000/js/core/merged-template-prepend.js"
-H "Host: cloud.example.net"
-> constant ~5.05 s, HTTP 200, 16186 bytes

curl measures 5 s, the browser 20 s for the same file -> looks like an aborted
response that the browser retries. Consistent with this: the external Caddy logged
error: "reading: unexpected EOF" / "context canceled" for this exact URI.

What I have verified

• Raw read of the file over NFS (cat): 10 ms
• gzip variant integrity (gunzip -t): OK
• strace of the PHP-FPM worker: PHP finishes the whole request
  (open, read, write response, shutdown, close) in ~3 ms
• Static files, status.php, index.php, theming CSS from appdata, API routes,
  and 404s are all fast (1-75 ms)
• Only this one existing appdata JS file is slow
• Ruled out: NFS locking, NFS/storage speed, DNS (incl. AAAA/IPv6),
  ClamAV reachability, Authentik/user_oidc reachability, gzip handling
• The aio-nextcloud container has no IPv6 on eth0 (IPv4 only)

Repair steps tried (no effect)

• Full container restart via StopContainers.php / StartContainers.php (no update)
• Full VM reboot
• Problem is persistent across both

Question
What in the internal Caddy/Apache chain could cause a single existing appdata
JS file to be streamed at ~800 byte/s while PHP-FPM itself responds in ~3 ms,
and how can this be fixed without updating to NC 33?

[szaimen]

Lets track this in #8138

[szaimen]

This is now released with v13.1.0 Beta. Testing and feedback is welcome! See https://github.com/nextcloud/all-in-one#how-to-switch-the-channel