SEGA Genesis 2 model PC BD MD2 VA0 USA 50/60HZ switch sound problem

Good day,
I decided to mod my SEGA Genesis 2 model PC BD MD2 VA0 USA my adding a region and a 50/60HZ switch. I used this guide and both switches seem to work.

How ever, I noticed some weird behavior, which I had not encountered before with all the other EURO PAL Mega Drive II which I have modded so far.

Any game (JPN/EUR/USA) I try to boot from the start at 50HZ, the music is either messed up, or the sound effects are missing. If I switch it back to 60HZ on the fly the music gets fixed, but in some games I have to reboot the console and restart it at 60HZ.

This even occurs in various European PAL region locked games like Mega Swiv, Mega Turrican, Ranger X & Alien Soldier. If I switch it to 60HZ right after it passes the region lock, they all work fine at 60HZ, but if I revert them back to 50HZ, the music gets messed up.

The only games which I was able to run natively at 50HZ right from the start and switched between 50/60HZ on the fly without any problems, were Bare Knuckle 1 (JPN), Turrican 1 (USA), Bio Hazard Battle (EURO) & Battle Squadron (USA). While Strider (USA) & Sensible Soccer (EURO), even though they start off fine at 50HZ, if I switch it to 60HZ during play, the screen gets garbled up, but if I switch it from 60HZ to 50HZ on the fly during play they’re fine.

Is this is a known issue with modded Genesis 2 consoles @50HZ, or have I done something horribly wrong? Is there any way to fix this and make it more compatible & universal like the EURO PAL modded Mega Drive II?

Thanks in advance
So, I re-soldered everything and checked the wiring / soldering and it seems to be ok, based on this guide for the Euro PAL MD2:

The problem persists and now I just noticed that the right audio channel is barely functional via RGB Scart Cable and only some sound effects are played from it even at 60HZ. (Its not a problem with the TV or the cable, as I verified it with another fully working un-modded PAL MD2)

I wonder if some capacitor/s blew up on the mother board in the process? I would hate hunting it down or changing all of them, as they're quite a few!

Well I'm out of ideas.