Problems-with-added-fields-in-3.1.0
From Joomla! Documentation
If you have a plugin that adds extra fields to the article editor it may break in 3.1.0. To fix this you must update to 3.1.1.
If you have a plugin that adds extra fields to the article editor it may break in 3.1.0. To fix this you must update to 3.1.1.