Nextcloud slow after new Data disk

I have a nextcloud install with all the data on a external disk (ext4) that is mounted in fstab.
Yesterday i replaced this (old) disk with a new one.
Before I made the swap, I copied all the files with the following command:
sudo cp -a /home/data/nextcloud/. /home/new/
All the files (also hidden) are copied with there permissions preserved. After that I mounted the new disk to the same location (/home/data/nextcloud/) in fstab and rebooted the server.
This all went ok, but now it takes more time to open files. In the gallery some folder thumbnails load slower and also opening the images is slow.
To be sure I did a occ files:scan.

What could be the reason for this behavior?

It looks a bit like Nextcloud has problems finding the thumbnails and photos. As opening them takes several seconds. The harddisk benchmarks show almost the same reading speed (old: 95 MB/s, new: 105 Mb/s).