Missing offline files

We use offline files for a few years now and it's working fine. A few weeks
ago some of our users noticed that synchronizing was very slow. Normally it
took seconds to check for differences, now it took minutes. They also
noticed they missed a large amount of their (offline) files.
I re-initialized the offline files cache (kb 230738) and created a new local
copy. The files are still missing. When I look with the explorer, tools,
folder options, offline files, view files I see all the files and most of
them say "local copy is incomplete".
I tested on another PC with another user and it works fine.
Does anyone have an idea what might be wrong and how to solve this?

Regards

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