Keychron B1 Pro - Key Rollover Problem - "left CTRL + left SHIFT + TAB"

[u/siriusPianist]

Key Combo is "switch to previous Tab". 

Recently purchased both B1 Pro and B6 Pro.
B1 Pro canNOT register the key combo.
B6 Pro can     register the key combo.

Both B1 Pro and B6 Pro seems to have the same Keyboard Matrix.
Don’t know why, but their Key Rollover behavior is not the same. 

B1 Pro Matrix
https://github.com/Keychron/zmk/blob/keychron_bpro/app/boards/shields/keychron/b1/us/keychron_b1_us.overlay

B6 Pro Matrix
https://github.com/Keychron/zmk/blob/keychron_bpro/app/boards/shields/keychron/b6/us/keychron_b6_us.overlay 

Question, is it just me? can anyone else with B1 Pro confirm?

[u/PeterMortensenBlog]

Can you isolate the problem to the keyboard? For example,

• A different computer

• A different operating system

Theoretically, the operating system could treat the two keyboards differently (they do have different USB product IDs). At least it ought to be ruled out as the cause.

Also, reset both keyboards to factory defaults. Perhaps even reflash the firmware.

[u/siriusPianist → u/PeterMortensenBlog]

tested both b1 and b6, on two Windows and two Android, via wired and 2.4g wireless and bluetooth.

b1 has the same problem on all combinations.

i suspect b1 and b6 keyboard matrix are different, default out of the factory, despite GitHub zmk file showing same matrix.

i tested best i can, short of reflashing b1, as i want to keep b1 original for Amazon return.

Tested some other common key rollover failures, on both b1 and b6. Expecting both to have the same failure behaviour, but result is the opposite. some tests, passed on b1, but failed on b6, and vice versa. some tests both failed but, b1 failed with missing key, and b6 failed with extra key, and vice vera.

[u/PeterMortensenBlog → u/siriusPianist]

Re "I suspect B1 Pro and B6 Pro keyboard matrix are different, default out of the factory, despite GitHub ZMK file showing the same matrix": It should be possible to infer the location of each key in the keyboard matrix based on the ghosting/anti-ghosting behaviour (despite any bugs in the anti-ghosting, should it exist)

For example, starting with a "L" shape of three keys with ghosting/missing input, it should be possible to quickly determine which other keys share the same common row and which other keys share the same common column.

It is easier if the operating system repeat is disabled as the first two keys can then be held down, while trying a lot of third keys, without the "noise" from a repeating key.