Cannot see local or s3 image asset source
For anyone else experiencing this issue, there wasn't actually any error shown in the Craft log file. Craft was trying to index the S3 access log files on the bucket and treating them as image files. Reindexing images didn't solve the issue either but I got my images back by deleting all entries from the craft_assetfiles table for files have the dateModified field set to NULL (these were not image files but Craft had added them to the table). [Solved by Craft Support]