I have installed Resharper recently and used the IntelliSense from this tool instead of the one built into Visual Studio.
I have encountered several critical problems with Resharper which forced me to uninstall it. I did however end up with a minor issue: the IntelliSense provided by Visual Studio no longer appeared automatically. I could still press Ctrl + Space and IntelliSense appeared but I find that quite annoying.
After a bit of searching around in the Visual Studio menu and settings, I have managed to turn it back on by going to Tools, selecting Options, then Text Editor and finally All Languages. Here Auto list members has to be selected and enabled. Even though this checkbox was grayed out, I could still de-select it and press OK. I opened the dialog box again, selected it again so that it’s checked and pressed OK again.
Hide advanced members is still grayed out and also disabled so I cannot change it, I don’t know why but it’s checked and IntelliSense works for me now automatically.