.ims files becoming corrupt

I am finding that my .ims files are getting corrupt. In the [Media Manager] tool (we are using team projects) I get files listed as "Offline: Importer cannot open". The list in there grows with time. These are files that have been working but stop working. There are two fixes for after this happens.

Option one (before I realised that it was the .ims files) I worked out that re-naming the .mov file and then relinking to it worked. Obviously, there was no .ims file with the new file name so it then was fine.

Option two is to delete the .ims file and re-start premiere.

Obviously, I would rather not have to do either, and it seems to be rather frequently a problem. I have just spent an hour working out which files are offline and deleting the relevant .ims file. I could have deleted them all but I feared how long it would then take to open the projected and re-generate them all.

Anyone else having this issue or worked out how to stop it happening?