Dear ,
Thank you for inspecting this issue. The problem is more insidious than it appears at first. As noted above, if you open and load the Sequence files into memory, it will mask the problem. Such is not an option in the main project with numerous files. Even if you delete and empty the entire contents of the Sequence files, save them, exit the the Editor and come back, the problem persists! As noted, the Reference Viewer is showing links at 4.18 that were garbage accumulated from previous deleted references. This is not a user error and is confirmed here in another bug report:
Even if the problem was simply missing links, can you imagine a web browser stuck, even after aborting the action?
Here I am providing even a simpler version of the BugReportV4.zip with just 2 Sequence files, and their contents are completely deleted and emptied. You will still get the hang, but Before you open and see the empty Sequence files. There seems to be no way for the user to fix these bug corrupted files as they are completely emptied from the UI.
This needs to be reported to the 4.18 people in charge of implementing the new Cross-level Actor References/Soft Object References. They need to catch the hang in their debugger with the source code.
Thank you for your patience.