When executing an executable (e.g. a setup or large programm) I have to wait until it's opened before I can continue opening other things (e.g. open a textfile or doc or another exe in same dir). It's like DO only can handle one task.
In Explorer I can run a setup and immediateley open a textfile and don't need to wait for the setup to be loaded.
Opus should run the program and then have nothing further to do with it, unless it's part of a batch operation (e.g. multiple things being run in a single button).
If something is blocking, I would suspect an antivirus scanner is scanning the exe before it allows Opus to launch it, and the antivirus tool is blocking other parts of the program from continuing until the scan is complete. (I've seen AV tools do the same with web browsers, locking up every tab in the browser when a download is scanned sometimes.)
But I do excact same things in Explorer and have no waiting-time (no files cached of course).
Edit: I noticed it today on a slow PC (w/o SSD, Win 10, Dual core).
Maybe the antivirus was tested more with Explorer than anything else. I can only guess, and speak from experience of seeing a/v scans on large installer exes lock up entire apps before, which is not specific to Opus.
Does it happen if you turn off the antivirus and test that way? If the antivirus is what's blocking things, then you may need to complain to the a/v vendor or switch to a better one.