You are correct, Carsten, that is indeed the case, but with the description on the file browser saying "AliFileCheck.File", no one can say for sure whether those files are missing the extension completely or whether there is an extension that is out of the ordinary, and hence the server disregards them.
Hence, the extensions of the files being omitted, doesn't help a lot.
The reason to revisit the subject is that I observed from the "error message.JPG" screenshot that on the right side, the Scope_5_1_dcp_22b0be9c-... is referring to a hexadecimal (probably UUID of a file, maybe the PKL) that is not appearing, even partially, on any asset of the DCP contents which are shown on the picture.
So, there might be a mix there that didn't let things work out. (Or more than one.)
My guess it that the problem was not with the version of the program, but with the procedure.