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If the Gallery is being refreshed from Cloud storage or Cloud backup, then during the refresh, esp. if there's a lot going on elsewhere on the connection or if the connection to the Web/Cloud servers is slow, then it may blank out briefly.
But if the Gallery is seemingly blank for a long time - over 2 minutes to 5 minutes at a time - then you have some other problem. (What version of the Gallery do you have, on what Android OS version, and how long does it remain blank at a time?)