CPU and Disk usage remains high after uploading large file tree

## Describe the bug
After uploading a large file tree with about `500 - 1000 files` nested in `4 - 6 directories`, ownCloud seems to be stuck in some kind of post-processing. The CPU usage remains high (50%) and ownCloud is constantly writing to disk at a high write speed (`~12 MB/s`).

By breaking the upload into smaller chunks and waiting a few minutes after each upload, the CPU and disk usage drops to almost zero eventually. Restarting ownCloud a few minutes after the upload has finished also sometimes solves the problem.

Messages of this kind are logged during upload:
`{"level":"warn","service":"frontend","pkg":"rhttp","traceid":"1dd3f77eb4917d0f404e48e16431e6ea","time":"2024-11-02T18:36:34+01:00","message":"core access token not set"}`

## Steps to reproduce
1. Upload a large file tree (~1000 files / depth of ~6)
2. Watch CPU and Disk usage ramp up (`htop`)
3. Do the same, but split the upload into smaller chunks and wait a few minutes after each upload
4. CPU and disk usage will drop after a few minutes.

## Expected behavior
CPU and disk usage should go down again after the upload has been finished.

## Actual behavior
CPU and disk usage stays high even after upload finished hours ago.

## Setup
Raspbery Pi 4B, 8GB RAM, installed on 512 GB external SSD using Ubuntu Server 64Bit.
ownCloud is installed bare metal.

```console
/usr/local/bin/ocis server
```