I decided to tun on the solution wide analysis.
However after 20 minutes it was still just saying "Loading caches" with no progress bar or spinning wheel.
While doing this it also stopped the usual file analysis from working (the coloured square is grayed out with a message "Analysis will start shortly")
To get the normal file analysis working again I had to
1) untick "Analyze errors in whole solution" in the Settings.
2) using the task manager I had to kill the processes named: JetBrains.ReSharper.ExternalProcessStorage.Process.exe
3) restart Visual Studio