Is this when closing a window, or when fully exiting via File / Exit Directory Opus?
If it's the latter, please link your account and then send a crash dump of Opus when in the frozen state to leo@gpsoft.com.au (or upload it to Google Drive, DropBox etc. and email a link to it).
You can generate the dump using Task Manager by right-clicking dopus.exe on the Details tab once it is in the frozen state. Choose the option to create a dump file, and it will tell you where it has placed it. It will be a large file but should compress down to a much smaller size.
Don't post a link to it on the forum as it may contain private information. (It will contain everything in memory that is part of the dopus.exe process.)