I do not know how, but when writing code, two panels open for suggestions and both are opened in a row. Unfortunately I couldn't find how to solve it.

These things sometimes be caused by plugins like CodeRush and Resharper that working together. I think it is necessary to use only one of these plugins. But I am not sure. The problem seems to be caused by the window being unable to be adjusted. You can follow these steps from Visual Studio.
Exit Visual Studio to be sure, then go back in.
When the same happens to me, update: In fact, the overlapping things are that both Resharper and IntelliSense show completion list after a character is typed. To prevent this, it is necessary to turn off either the Resharper or IntelliSense related feature. I prefered to close IntelliSense's completion list with help from this site. For this, I followed these steps:
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