Multiple modifier keys with Mod-Tap

[JosNun]

Heyo!

I'm trying to customize my base layer keymap as described here, and I can't seem to get it to build properly. My goal is to have holding G and H press all the modifier keys (super, ctrl, alt, and shift).

Here is what my custom_config.h looks like:

#define MIRYOKU_LAYER_BASE \
&kp Q,             &kp W,             &kp E,             &kp R,             &kp T,                                      &kp Y,                                &kp U,             &kp I,             &kp O,             &kp P,             \
U_MT(LGUI, A),     U_MT(LALT, S),     U_MT(LCTRL, D),    U_MT(LSHFT, F),    &kp U_MT(LG(LA(LC(LSHFT))), G),             &kp U_MT(RG(RA(RC(RSHFT))), H),       U_MT(RSHFT, J),    U_MT(RCTRL, K),    U_MT(RALT, L),     U_MT(RGUI, SQT),   \
U_LT(U_BUTTON, Z), U_MT(RALT, X),     &kp C,             &kp V,             &kp B,                                      &kp N,                                &kp M,             &kp COMMA,         U_MT(RALT, DOT),   U_LT(U_BUTTON, SLASH),\
U_NP,              U_NP,              U_LT(U_MEDIA, ESC),U_LT(U_NAV, SPACE),U_LT(U_MOUSE, TAB),                         U_LT(U_SYM, RET),  U_LT(U_NUM, BSPC), U_LT(U_FUN, DEL),  U_NP,              U_NP

For reference, the repo is here: https://github.com/JosNun/miryoku_zmk

The failed build job (with stack trace) is here: https://github.com/JosNun/miryoku_zmk/actions/runs/12857264695

Interestingly, the firmware for the right half of the keyboard builds fine. I'm not sure if the keymap lands on that half, though, since that's the remote half, and the left one is the master?

U_MT(LG(LA(LC(LSHFT))), G) is what my keycode (not sure if that's the right term?) is for the key, but I'm not sure if that's the right syntax, or if there's something else I should be using? Maybe the U_MT behavior itself can't handle multiple modifiers?

Any pointers for a direction to look next would be greatly appreciated!