I think the (__MACOSX/OEBPS/._template.css) files are invisible files the macs leaves behind. I see ._store files left around in every directory that the macs open. I think files with dot underscore are invisible to the macs. So they exist but because you can't see it it would stuff up the inventory.
Just a wild guess, but worth following up.
Edit: Another thought. The dot underscore file would have been created when you edited the OPF. Indesign wouldn't have written it. Try epubchecking before you open the epub and see if you get the same error. If you don't, then edit it and if you get the same error ask the mac community how they do it.
found this link for you. hope it helps. https://www.mobileread.com/forums/showthread.php?t=55681