Freezing at research section remains.
Version: 2.9.9.8 Beta (984254) 64-bit - 12 7 2020 + Windows 10 (Korean)
I made small .mp4 file.
That looks like it could be an issue with the file rather than the program. Does it only freeze when you click on that one document, or with other documents as well? If you were to remove that document from your project (delete it from the Trash as well), does that solve the issue?
What document type is that you tried to open?