In Classic view, when merging to PDF, if there is a corrupt file or other problem, you are given an error message that identifies the file that is a problem, which allows you to easily remove it and redo the merge. In SKY you just get an error message, with no explanation of what the problem is (and it's a persistent error message that doesn't go away until you click it). Please bring back the details of the error so we can troubleshoot when merging!
If certain documents cannot be merged, the Merge to PDF action now informs you which documents are causing the problem and makes it possible to remove them. Thank you everyone who pointed out this issue.