Hi,
Well, today, I didn't had the 500 error, so I couldn't look into it.
However, I could see the website so I could check the frontend situation and the backend settings. I was also able to access the FTP, so I was finally hoping to be able to look into it.
However, the components/com_hikashop folder has been configured to not be readable:
i.imgur.com/CrolAFw.png
So I wasn't able to access it to add the necessary debug in the files involved with the routing, which is where I think is the problem.
Could you check the permissions of that folder so that the FTP account you provided can access that folder ?