That was me, and the thread was:
Every time you save your schematic in KiCad V5 it should re-create the [project]-cache.lib file, if the original libraries are still available. If neither are available, then KiCad V5 also can not show the schematic and all symbols look like [??]. If the project has never been resqued (for example from KiCad V4), then the rescue library probably does not exist at all.
I do not understand. It should only do this once during the first import. What is the exact message? (… Thinking a bit…) (A little bit later) KiCad V7 (or V8) is probably displaying a message that the library is missing. As long as the schematic itself looks OK (I.e. it does not show [??] instead of the real symbols), then this is a very small thing and easy to fix. The simplest and quickest is: Schematic Editor / File / Export / Symbols to new Library. Make it project specific and also accept it when KiCad asks: Update symbols in schematic to refer to new library?.
The other method is to use Schematic Editor / Tools / Edit Symbol Library Links and then create references to the new library.
(Getting a bit technical, skip if not interested)
The third method I would have to think about some more. In itself, it does not matter much if KiCad is referencing to some none existent library. If that library does not exist, then KiCad can not update from it anyway, so there is also no way it damages the schematic. It may be preferable if KiCad did not complain about this at all when a schematic is opened. Maybe it’s better if KiCad only does this during some explicit library management, such as a menu option in the Tools menu.
(After some more thoughts…).
I am reasonably certain that KiCad V7 imported the symbols from the [project]-cache.lib during the V5 to V7 conversion, and these symbols are now embedded into the KiCad V7 schematic itself. (They must be embedded if KiCad is able to show the symbols). References to the old `[project]-rescue.lib’ are just a (minor) inconvenience, they are not a real problem.
Problems like this only exist when converting old projects. As soon as a project is saved in the KiCad V6 or newer formats, it does not happen anymore. (But the links to the old rescue library stay in the schematic until you manually fix those links.