I think you need tech support’s help on this one. when you copy from the original location, your embedded fields maybe corrupted, and when you unformat - the record numbers are not matching those of the library on the other computer. changing from X7 to X5 (or X8 to X5 maybe part of the problem… Clarivate support may be your best resource.
Can you try changing your endnote preferences to use the “accession number” field rather than the record number field?
Do you have access to the original computer and library? How did you move the library from A to B computers?