Change 1000+ of WordPress Featured Images in 5 Minutes! › Forums › Questions and Answers › Take the first external post image Symbol bug › Reply To: Take the first external post image Symbol bug
I think shorter image file names (max. 255 bytes) are a good way to be able to use bulk edit again.
Or use a plugin for external featured images and set the images manually or via Bulk Edit. This plugin supports both the free plugins Featured Images By URL (at wordpress.org) and Featured Images From URL (at wordpress.org).