The Add to Feedly plugin by “davidmerinas” is known to cause some problems with editing in the LiveEditor, particularly the loading of some popup/lightboxes for editing content.
This can be fixed by going to OptimizePress > Support > Disable Styles & Scripts > Plugin Styles & Scripts > Disable for back-end (LiveEditor)
Next, tick the box in the “JS” column to disable the javascript from this plugin from rendering inside the LiveEditor
Save the Settings after making this change and reload your page in the LiveEditor and the content should be editable.