API returns blank response after installing & uninstalling WP-rest-api plugin

Question

The WordPress/WooCommerce API is broken on my site: http://example.com/wp-json/wp/v2/posts and http://example.com/wp-json/wc/v2/products both return a blank response.

Running a Python request by

response = requests.get('http://<mysite>.com/wp-json/wp/v2/posts', auth=HTTPBasicAuth(*auth))

gives a response (examined in a debugger) of

{
   ...
   _content: b''
   headers: ... 'content-type': 'text/html' ...
}

According to https://github.com/WP-API/WP-API/issues/2911, the blank response means there is an fatal php error.

Last week I was using the WordPress API to add WC products to my site, with no problems. I believe it stopped working when I installed the WordPress-rest-api plugin, then uninstalled it, after realizing it was not necessary.

I set up a development site as a sanity check and everything worked fine.

Specifically, I want the WooCommerce API to work, but I assume that means the rest API should also work.

We have backups, but there have been some changes since the last backup. Do I have to recreate the site from backup for it to work again?

EDIT: The only error in error_log is

[PHP Deprecated:  Automatically populating $HTTP_RAW_POST_DATA is 
deprecated and will be removed in a future version.
To avoid this warning set 'always_populate_raw_post_data' to '-1' 
in php.ini and use the php://input stream instead.
in Unknown on line 0

which does NOT occur at the same times as my API requests.

Answer 1

Uninstalling and reinstalling all plugins revealed the answer, which I recommend as the first step for addressing this sort of problem.

The problem was apparently due to a conflict between WC-Vendors and another plugin which declared the same class WC_Email_Notify_Shipped. So I disabled WC-Vendors, which we weren't using at the time.