A number of reasons could cause this. First I suggest you check your Internet connection to find out if there is a problem with the speed and ping, or if you are experiencing intermittent issues (your Internet service going on and off at short intervals). Ping is more desirable at 60 or a smaller number. Unreliable Internet service can result in no preview. Also insufficient computer memory can cause this issue. However, you will observe this by other applications hanging, opening very slowly or frequently popping up error messages.
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