This is less a problem than something to be aware of. When using Shotcut (iMac, 2.5GHz Core i5, 12GB of memory, High Sierra) I’ve noticed at times that what’s in a folder I’m working in isn’t always reflected when you go to the Open File dialog.
At first I thought I mislaid the files, though going back to the Finder there’re there, it just seems to take awhile for Shotcut to “see” them.
A way around this I have found is to open one or two random folders (via Shotcut’s Open File dialog). By the time you get back to the one you actually working in, Shotcut “sees” its content and all is good.
And I’ve also noticed that Shotcut is more than a little bit crashy (I’ll typically get at least two or three on any given day).
Though that’s relatively minor in that it doesn’t stop me from doing whatever I need to do and perhaps more importantly, It reminds me that I need to “Save” and do so often.