Thumbnails re-created after migrating from OC to NC

Hi everyone!

Recently I migrated from OC 9.1 to NC 11.0.3. Migration worked very well. No issues there.

Except when it comes to thumbnail creation of images:
For photos / images which were already existant in the OC installation, it seems like NC is creating the thumbnails again. I believe it is doing that because loading the thumbnails for the first time takes very long - even significantly longer than on OC. Loading one thumbnail the first time on NC takes up to 5 seconds.

So my questions are:

  • Can anybody confirm that NC is creating again thumbnails for images which were already existant in the OC installation?
  • And why is it doing that again?
  • Is it known that the thumbnail creation process is much slower than on OC?
  • And do I have now two sets of thumbnails for each image on my HDD? One from the OC installation and a new set from NC?


Here is some more information after getting deeper into that:

It seems that during the migration all thumbnails have been deleted from the HDD.

Is this intended to happen?