Hi Stuart,
I really don't know the root cause but there is related issue fixed(?!) in FP4:
So I believe you shouldn't use this special table in reports and create your own query to display approval task comments.
It could be helpful if you take a look at the query LiteRequestApprovalComments to understand how to get the value(-s) of approval comments. Actually it's the task history field HISTORY_DESC with filter APPROVAL_COMMENTS = 1.
Gytis