I know I sound like a broken record here, but there is only one organization that can help you with problems with SkySight, and that is SkySight support.
It is commercial software for which you are entitled to support - you don't need to ask randoms on internet forums.
Please contact
skys...@skysight.io with your problematic waypoint file, reproduction steps and details about your device/browser.
CUP files are a common problem, because for reasons unclear to me there are wildly invalid CUP files scattered around the internet, either edited by hand or generated by faulty software which require so much special casing and exception handling they are not always possible to process. The other issue is users uploading enormous waypoint files which we restrict because the impact on load time and interactivity becomes significant.