RGB matrix animations not propagating correctly with split keyboard

[linkpy]

using keymap : https://github.com/linkpy/vial-qmk/tree/vial/keyboards/splitkb/aurora/sofle_v2/keymaps/vial

i enabled rgb matrix animations and for example for the reactive solid splash one, pressing a key on the right hand will make the splash animation propagate to the left hand, but not the other way around: the animation doesnt propagate to the right hand when i press a key on the left hand.

to reproduice

• enable rgb matrix and solid (multi)splash (for example but the issue happen with all reactive animations that propagate to the other hand)
• set the animation to solid splash
• press a key on the right hand and notice the animation propagates correctly to the left hand
• press a key on the left hand and notice the animation doesnt propagate to the right hand

example :

vid.mov

(note: in this video the left hand doesnt have backlight leds but only underglow one)

[lesshonor]

Have you verified that this does work in vanilla QMK with identical configs?
I only see one split data sync configuration setting set, and it wouldn't affect RGB.

[linkpy]

oh damn i had no idea these configuration existed.
i am unable to try now but in the evening i'll give a try to SPLIT_TRANSPORT_MIRROR (which seems to be what i want).