[tlug] The File That Was/Wasn't There

[CL <az.4tlug@example.com>]

Got a bit of a head scratcher (for me, at least):

BASICS:

Lubuntu 18.x,
Double Commander file manager, my preferred manager which I would 
normally highly recommend
PCManFM-Qt file manager, the standard almost-good-enough-but-never-quite 
file manager that comes with Lubuntu

I downloaded a folder containing:

a *.txt file of 30kb
a *.exe file of 99kb
a *.mkv file of 2.7Gb

to an NTFC-formatted external disk.

WHAT HAPPENS:

Except, only the first two files are visible to my preferred file 
manager, Double Commander.  I have been through the configuration files 
and find nothing that makes this file visible.  This is the first and 
only instance of this problem for me.  Double Commander is set up via an 
"Options" menu that creates a unique *.conf file.

If I view the same folder in PCManFM-Qt, all three files are visible and 
the *.mkv file is playable.  PCManFM-Qt uses the more standard (WIN / 
*buntu) setup of Edit > Preferences.

WHAT I'VE TRIED:

I tried copying the file to an ext4-formatted disk.
I've looked into all "Show Files" options.
I've checked and compared how the two programs report file and folder 
properties.
I asked in Double Commander's forums.
And the file still isn't visible.

Can anyone think of ANY attribute I may be missing here? This is one of 
those little niggles that ruins the big picture until you finally figure 
it out.  This is the ONLY instance of the problem in two years of using 
Double Commander and it is driving me crazy.