I store some of the projects in my solutions on an external SSD. If I load up the solution having forgotten to plug in the drive, unsurprisingly Resharper displays a lot of red in the source. What is surprising though, is that this appears to permanently invalidate the cache. If I plug in the drive and reload (or close and reopen) the solution, it begins an 'Updating source files' pass on the project's source code again.
I would think it should be possible to differentiate between a change in the source and source being inaccessible, and so prevent the cached data from being immediately dropped? Could you perhaps add an option to retain cached data for files for a short period/number of reloads, so that it could be enabled again if the files are once again available?
It's possible that dealing with this may be harder than I first thought, but still it seems somewhat heavy handed to just dump everything permanently immediately on failing to find the code.