Another mysterious "Lost communication with MCU 'mcu' and 'mmu' and 'EBB'"

[warm palm]

Hello all, I'm running VC3.1 on RPi4B+, Octopus PRO, Fysetc ERB V1 (ERCF), EBB36 and 1080p usb webcam.
All "big" things (servos, RPi etc) are powered off dedicated 24V-5V stepdown.
Recently I added EBB36, fixed problems with shutdowns due to EBB overheating and all was looking great.
But I started getting "Lost communication with MCU '....'" error - all three MCUs lose communications at random. Webcam shutdown with "NO SIGNAL" on screen as well.
Things I've done:
Replaced EBB36 USB cable and fixed it so it is basically one solid part with EBB
I thought the USB hub on RPi was maybe crowded so I disconnected webcam

So far I have 4-5 shutdowns and 2 webcam disconnects in 10 hours of actual printing

Quick fixes to do:
Replace RPi4B+
Replace USB cables going from RPi to Octopus and ERCF

I found this https://discord.com/channels/582187371529764864/1193324445826297998
which seems to have the same issue. I do not understand the fix there completely (*connecting all ground terminals between PSUs and wiring *)

I am mainly writing to ask if there's a known reason for these problems before I start playing whack'a'mole with potential solutions.

[lavish flicker]

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[vagrant ibex]

Have you found a solution to this problem?

[warm palm]

I added anouther ground to RPi... I have no idea if it helped or if I the issue is simply not showing up in the meantime.... @vagrant ibex