I’m having a similar issue, but without any plugins. Not sure why the 403 is happening. I go to edit content and I get a dialogue box saying ‘An unexpected error has occurred’.
What does that dialogue box look like? Could you please post a screenshot?
Please also tell us what your hosting provider is.
Isn’t this a duplicate of this post: “An unexpected error occurred” when editing+saving content, even as Admin ? Feel free to reopen if it isn’t.
Sorry, I thought it was just a comment on the original post.
For some unknown reason, I’ve come back to the issue a week later and it’s fixed itself! I honestly have no idea why, but I would be sharing a screenshot of the dialogue box otherwise. I will come back if it occurs again.