The WP50NB40 drive is not UHD capable unless it has been cross-flashed. You've only done half the job. Now do the cross-flash. BU40N 1.00 is the recommended firmware.
Actually, perhaps its the cross-flash that is not taking.
The tool reports it works:
.\makemkvcon64.exe f --all-yes -d E: rawflash -i "DE_LG_BU40N_1.00.bin"
Reading input file DE_LG_BU40N_1.00.bin
Flashing flags = 0x0 : 0 0 0 0 : ---- ---- ---- ----
Current Drive ID: HL-DT-ST_BD-RE_WP50NB40_1.03_212005070929_SIM2121673205
Using USB chipset workaround for Desktop drive handshake
Ready to write drive flash memory. (auto confirmed)
Operation started: Sending flash image to drive
100% Operation finished
Operation started: Programming flash
100% Operation finished
Done successfully
However MakeMKV still reports 1.03 (is this expected?)
LibreDrive Information
Status: Enabled
Drive platform: MT1959
Firmware type: Patched (microcode access re-enabled)
Firmware version: 1.03
Apologies for all the posts. I got it working using the proper recovery mode flashing in the tool. I was selecting the wrong order when picking the firmware versions.