I don't know what caused and when it exactly happened on me. When I clicked on the File menu button, it gives nothing. No item showed up and expanded. However, it was working when I initially opened the TeXStudio and all the other menu buttons work (Edit sometimes didn't work as well).
I have tried restarting the program, it works at the beginning, after compiling my TeX files in a few minutes, the File menu didn't expand again.
Windows 10, TeXStudio 2.12.6.
PS: the Open File icon works, just the File menu didn't expand.
I don't seem to get this bug on Windows 7 but the context menu (right click) has a similar issue. After some time it won't pop up anymore. Restarting the program fixes this for a few minutes.
Last edit: Toto 2017-08-02
The same problem happens to me.
After some compilations or some time, not sure which unlocks the bug, File menu doesn't expand anymore.
I need to close TexStudio and restart it.
Windows 10.
TeXstudio 2.12.6 (hg 6632:7777b2b8a906)
Utilizando Qt Versão 5.9.1, compilado com Qt 5.9.1 R