Calibre starts only in debug mode?

Trying to run Calibre 0n Windows 10, 64-bit, all latest updates applied.

When I run Calibre, I briefly see a blank application window, which then disappears.

If I run as Kovid suggests, in debug mode i.e. calibre-debug -g, Calibre starts and runs with no errors, and no indication (to me at least :) ) of why it fails to run normally.

Any thoughts on this?

C:\WINDOWS\system32>calibre-debug -g
calibre 4.23 [64bit] embedded-python: True is64bit: True
Windows-10-10.0.19041-SP0 Windows ('64bit', 'WindowsPE')
('Windows', '10', '10.0.19041')
Python 2.7.16+
Windows: ('10', '10.0.19041', 'SP0', u'Multiprocessor Free')
Interface language: None
Turning on automatic hidpi scaling
Registering with default programs...
devicePixelRatio: 1.0
logicalDpi: 96.0 x 96.0
physicalDpi: 96.0 x 95.8490566038
Using calibre Qt style: True
Registered with default programs in 2.4 seconds
[0.00] Starting up...
[0.02] Showing splash screen...
[0.28] splash screen shown
[0.28] Initializing db...
[0.45] db initialized
[0.45] Constructing main UI...
[3.67] main UI initialized...
[3.67] Hiding splash screen
[4.62] splash screen hidden
[4.62] Started up in 4.62 seconds with 2288 books