Does this only happen with pictures on your micro SD card? Or does it happen with pictures on the internal hard drive as well? You could have a corrupted micro SD card. This has happened to me before. Fixed it with a new micro SD card.
I have used the internal memory as well with the SD card removed from the tablet, so this can be excluded.
I have also cleared the cache and all the settings of Gallery several times, but the problem returns every time again.
However, I have found a 'work-around' for the app. Quickpic: I have moved all videos with the extension *.mov to a different folder and excluded it from scanning by the app.
Now all thumbnails are created, and do not disappear any more!!! :)
So the *.mov files probably cause problems in the 10FHD (only with Android 4.3) when thumbnails are created.
This "selective scanning" cannot be arranged with the standard app Gallery because it cannot be configured to select folders, so everything (including the videos) is scanned by default.
For me is it quite simple: I do not use Gallery any more, until a firmware upgrade of the tablet will fix it.
Quickpic is much better to work with, anyway.
So this problem is (for me) fixed with this work-around, and I am able to use my tablet again!
Another (less important) issue that I have discovered today is that the app GOOGLE AGENDA (standard app on the tablet) cannot be configured with a notification sound: it is set to silent as a standard, and the app crashes (:headwall02:) when another sound is selected.......
Quickpic is a great alternative to the stock Gallery app.
Try these builds of XBMC. HD is working perfect on the tablet but streaming thru HDMI is still choppy
http://mirrors.xbmc.org/nightlies/android/x86/
I have discovered that all videos made with my Canon camera (SX240HS) cause the 'thumbnail' problems.
Other *.mov files made with my Smartphone (Sony Xperia U) are 'safe' and do not cause any trouble.
I have removed all Canon- *.mov files from my tablet and micro SD card, and now ALL APP's (Quickpic, Gallery, ASUS studio, Photos) work without any problem!!! :):)
So I wonder if anyone can reproduce this situation... I assume that more Canon cameras use the same file format which is apparently not compatible with this tablet (after the upgrade to Android 4.3).
So I have send my tablet to the service center twice without any results... they are probably not aware of this bug.
I will phone the contect center in The Netherlands next week to tell them what I have found, and hopefully they will notify the ASUS development team to create a bug fix.