Today scan functions were bypassed (see bug 92478) in 64 bits Windows version.
I use for photos irfanwiew 64 bits and i see it is able to scan with TWAIN or WIA interface without problems
So with task manager i have checked what process it starts for scanning
in fact it is simple when scan is started:
irfanwiew 64 start a 32 bit stub which control a 32 bit subprocess which contains portion of irfanview 32 bit code dedicated to scan functions
Why not use same method in 64 bits Win LO start a 32 bits stub which use portion of code 32 bits win LO which control scan functions ?
I think this is only method because Windows does not provide 64 bits TWAIN interface
Rereading tdf#92478, I noticed 2 things:
1) this tracker could be a dup of tdf#101066
2) https://bugs.documentfoundation.org/show_bug.cgi?id=92478#c29 advices to retrieve TWAINDSM.DLL, perhaps you can give it a try?
Another interesting comment here:
64-bit TWAIN 2.3 drivers for Windows are not widely implemented. While we've added support to use TWAINDSM.DLL 64-bit driver --in practice we have no Scan support for 64-bit Windows builds.
Implementing support for 64-bit WIA framework would allow use of widely available 64-bit scanner drivers. 
32-bit TWAIN drivers remain common, but providing 32-bit WIA should probably be implemented as well. WIA is stable enough on Windows that TWAIN could be deprecated.
*** Bug 106770 has been marked as a duplicate of this bug. ***
*** Bug 101066 has been marked as a duplicate of this bug. ***
this should be Windows only, TWAIN would remain viable for macOS and Linux
*** Bug 111407 has been marked as a duplicate of this bug. ***
*** Bug 114635 has been marked as a duplicate of this bug. ***
A pointer to a one-function-does-it-all for potential implementers:
When i scan from an 64 bit application with WIA driver
i can see that WIA 64 bit driver start a 32 bit subtask
which with WIA 32 bit driver make the scan and after return image to main task.
So Even Microsoft recognize that scanner manufacturers don't often provide 64 bit drivers and use this strategy as workaround.
So i continue to think that for 64 bit LO the only solutions are:
1) when select source select only WIA mode and ignore TWAIN
2) start a 32 bit subtask which use 32 bits LO scan code and return obtained image to main task
*** Bug 118079 has been marked as a duplicate of this bug. ***
*** Bug 119816 has been marked as a duplicate of this bug. ***
Let's simplify the summary, TWAIN works well thanks to Mike K. but is dependent on 3rd party TWAIN support. Issue here requires a native Windows os implementation of MS Windows Image Acquisition framework where os scanner driver support is more common.