Errors and warnings can be shown in the Preview and publish step (T260134). These are shown in a message box and navigation controls are provided when multiple issues occur:

Based on T260134#7713538 the navigation controls need some adjustments:

• Include a counter of the issues. At 8px from the arrows.
• Separate the arrows. The buttons should be 24px apart.
• Also, display as disabled the arrows when there is no previous or next element.

(note that the missing icon issue marked as 1 is covered on a separate task: T302789)