Do you have both Sw versions on the same machine? Maybe it's a version conflict. In general, we don't keep an old version precisely because of the conflict between the links that point between the different versions.
It is likely that it is a problem with a corrupted options file, necessarily directly from the part,
You can try to open it from solidworks Rx (type RX in the start menu, launch Rx 2020 and at the very bottom "launch solidworks ignoring the settings under tools/options) and try to open the file,
I think you could possibly attach the piece in question so that we can try to open it,