Something went wrong with the plugin API.

This may be a plugin conflict. First off, try to disable all plugins. If the problem goes away, enable them one by one to identify the source of your troubles.

You can also try manually installing plugins/theme:
Try installing or upgrading the Plugin manually.
Try installing or upgrading the Theme manually.
https://www.wpbeginner.com/beginners-guide/how-to-manually-update-wordpress-plugins-via-ftp/

• This reply was modified 4 years, 10 months ago by t-p.