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Not sure what caused the issue, it is pretty weird. It looks like all you can see is field names.
I can offer you to check if this is solution with your admin or maybe the problem is deeper like in database or something.
You can try to edit products by means of desktop application called Store Manager for Magento. It works directly with database, so if you be able to edit your products via this app, it will mean that probably you have the issue with your backend. If the issue remains, it would most likely indicate that you have to dig for some more serious issue.
In any case, here is free trial of Store Manager available for use for 2 weeks -
Hope it will point you in the right direction. If any users have faced such issues, you\’re welcome to share your experience.