500 error on all config/media pages

I've got an issue with the image styles and uploaded files on my site:
I was running drupal 8.1.1, and a few days ago discovered that all pages under admin/config/media/ result in aan 500 internal server error.
Then I updated drupal to 8.2.3 yesterday, and it seemed to fix the problem. But today, it's giving me the same 500 internal server error again. Even if i replace the drupal files.

The error is:

Internal Server Error

The server encountered an internal error or misconfiguration and was unable to complete your request.

Please contact the server administrator at webmaster@site.com to inform them of the time this error occurred, and the actions you performed just before this error.

More information about this error may be available in the server error log.

Additionally, a 500 Internal Server Error error was encountered while trying to use an ErrorDocument to handle the request.

Apache Server at www.stcaecilia.com Port 80

The server error log gives me this:

[Mon Nov 21 15:43:59.942238 2016] [core:error] [pid 323836] [client xx.xxx.xxx.xx:xxxxx] AH00124: Request exceeded the limit of 10 internal redirects due to probable configuration error. Use 'LimitInternalRecursion' to increase the limit if necessary. Use 'LogLevel debug' to get a backtrace., referer: http://www.stcaecilia.com/en/admin/config

Enabling or disabling error messages doesn't give me any aditional info.
Any clues?