The IDE IntelliSense boxes that display when hovering on variables, functions etc. on the right hand side of the screen are running beyond the screen limits on my laptop. Sometimes the box displays correctly for a frame or two before shitfing right into a new position and remaining there. Much/most of the text within disappears beyond the screen edge rendering the box largely useless.
Disabling Visual Assist cures this problem and the IDE displays the same box with its right edge correctly aligned to the screen edge.
This problem was present in build 2389 and remains in build 2393.
This is happening with Visual Studio 2015 Professional on Windows 10 Home with a screen resolution of 1366 x 768 (and no windows zoom enabled). Screens attached. The second screen (with the _IDE suffix) was taken with Visual Assist disabled from the menu and shows the correct behaviour.
I am sorry you are having this issue. I remember we reported a very similar issue to Microsoft for VS 2019 and they fixed it. I suppose upgrading might not be an option. Can you reproduce it fairly reliably? It is interesting and unexpected that the issue goes away when you disable Visual Assist.
This happens almost all of the time for any box that's wide enough to need clipping to the screen boundary. I also thought it strange that it only occurs with VA enabled.
I'm not sure if it's related to my limited screen space. I don't have access to my external displays just at the moment to check behaviour at higher resolutions. If that situation changes I'll update here with my findings. I don't recall seeing it before at 1920x1080 or better, but I haven't done any coding for a few months so I really don't remember.
If it's a Microsoft problem then I guess I'll have to live with it anyway given the lack of support for 2015 now.