That may depend upon caching in the engine and the number of tracks regardless of version. While you can have hundreds of clip objects in the playlist and timeline, we cannot keep all of the files open as processes are limited in how many open files they can have. Also, along with the open files is other memory structures including sometimes images, and we need to keep memory usage low. So, the internals of some of these objects including file handles are cached so that only the N most recently used are held open and in memory. N depends on the number of tracks and version of software, but currently is it is 2 * (N+1). It is never always possible to act as if the file is always there when it is actually not. On Linux, when you delete a file that Shotcut has open, you can still use it as it still on disk until something overwrites or zeroes it. On Windows, it is locked - at least on NTFS - preventing you from deleting it.
That said, with a quick test, I did not yet reproduce it, and I will try more later. If the file is gone when trying to restore the uncached clip object, Shotcut needs to try handle it without crashing. Per the engine default configure, this would show as white frames. It does not show “INVALID” until the project is reloaded and the missing files ignored.