Would you be able to post a quick photo of the problem. I would like to help but since there a number of factors that can cause the issue you describe a photo would be helpful if possible. The Royal Icing may have been too stiff/dry when it was piped on, it may not have dried properly due to humidity or it's also possible that your decorations were not 'structurally sound' (for example, if you pipe a long string of Royal Icing, it will often crack unless it has sufficient thickness to support itself. Hope this helps.
Regards,
-Adam
