I don't believe they changed the save format on consoles. Those should still import from SRIV to GOOH correctly. The save format was changed to support Steam Workshop which is only on PC.They changed the format of the save files in SRIV, making them incompatible with GOOH. Your old boss is used because there's a save somewhere on your system that's compatible. There's no fix for this, and it's not been patched. The same thing happens on the console versions too.
It works quite well.Maybe this will work, although I haven't tried it myself:
https://www.saintsrowmods.com/forum/threads/import-boss-from-sr4-to-gooh.14763/page-3#post-98622