Curious AppData problem

My AppData folder is about 1.7 Gb and has the usual three subfolders (Local, LocalLow and Roaming). I sometimes copy the whole or part of it for backup reasons. However, I cannot do so now because when I try to take a copy, it says the move will be only 345MB, and that is what it copies, stopping well short. I have investigated permissions etc and found nothing amiss. The problem is in the Local folder, although I can copy all its sub-files separately.

What is really extraordinary is that if I access the AppData folder from another PC across my home network, I can copy the full 1.7Gb!

Any ideas?

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