Sadly that is normal. The more pictures there are in a folder, the less responsive Explorer becomes in thumbnail mode. In fact, it has a hard limit of 4,096 files. Only the first 4K files that are displayed (from any point in the folder) have thumbnails generated; the remaining pictures are left blank and no thumbnail is generated for them.
There are few options (in order of likeliness to help):
- You can try is to use TweakUI to reduce the size and/or quality of thumbnails under
- You can try toggling thumbnail caching in Explorer (
Tools->Folder Options->View->Do not cache thumbnails) Enable it if it is off or disable it if it is on.
- You can try putting the picture files on a faster drive (Explorer has to open and read them all).
- You can try deleting the
thumbs.db file in the folder to force a refresh.
- You can try rebuilding the icon cache in TweakUI (
Repair->Rebuilt Icons), though technically it shouldn’t affect thumbnails.
- You can try configuring Explorer windows to open in separate processes (
Tools->Folder Options->View->Launch folder windows in a separate process), or not do so if it already is.
- You can try just waiting and waiting, but it may simply be stuck.
Unfortunately there is no simple cure to getting thumbnail mode to work efficiently and effectively. You have to see what ends up working for your particular use-case. It is better in Windows 7 (as compared to XP), but even there it is still not the best.