Problem:
toolset form - edit post - featured image validation

Solution:
With Toolset Forms version 2.6.9 we already shared a hotfix to should fix the image validation field.

Relevant Documentation:

Problem: I would like to export content from one site and import it in another site. The content includes multiple custom post types, their custom fields, taxonomies, and post relationships. When I import this content into another site, I see error messages in Toolset > Import > Associations tab stating that many of my post relationships cannot be imported. "Missing: Can't Find Intermediary Post with GUID" -and- "Missing: Can't Find Intermediary Post with Title" appears for these posts.

Solution: In this case the errors are all shown for M2M post relationships. These relationships are established using an intermediary custom post type. That post must be exported along with the two other custom posts in the post relationship. You may need to turn on the visibility of those intermediary post types to be able to export them. After exporting from the old site and importing those intermediary posts in the new site, the association process in Toolset > Import > Association tab should be able to find all the missing intermediary posts and migrate the post relationships successfully.