Removing the post voting plugin will leave reviewables with type ReviewablePostVotingComment in the queue and attemping to access the review queue will crash with a 500 server error and the message below.
It seems that the fix proposed here was either not implemented or has regressed.
ActiveRecord::SubclassNotFound (The single-table inheritance mechanism failed to locate the subclass: 'ReviewablePostVotingComment'. This error is raised because the column 'type' is reserved for storing the class in case of inheritance. Please rename this column if you didn't intend it to be used for storing the inheritance class or overwrite Reviewable.inheritance_column to use another column for that information.)
Workaround/fix:
Reviewable.where(target_type: 'PostVotingComment').delete_all