Hi,

yes, the Leds are driven by a STM32, with a 3.3 to 5V converter.
They are working in whitewood with the correct colors as expected, and also working well in MPF.
But activating the flipper impacts the led colors and seem to 'disconnect' them from the STM32, as if the data line was reacting.
The wire is less than 15 cm between the converter and the first led.
I'll give a try about the suggestions mentioned.
STM32's are on 2.0.x firmware, where there modifications in the recent firmwares about that ?
Could you confirm the gen2test python command to upgrade directly the opp firmware without having to put the serial interface ?

thanks again

Indeed, I'm leaning to a GND interference.
I have diodes on the coils, but the ground are common with STM and 24V. I'm not sure about the meaning of inverse diodes ?
I'll isolate a specific ground for the leds.
the wire for the neopixels is surrounded by plenty of wires, but switches mostly, but the flipper coils are in the vicinity (around 20cm, so I may end by dedicating a STM solely for lights to avoid interference

do you confirm that I can upgrade the firmware through gen2test.py ? or maybe it's an old pre-STM32 leftover ?

then do I need to put back the serial interface for flashing the new firmware??

Ok, so I've updated the STM32 with the serial. Was feasible but did no change anything in the actual behavior
Then I've modified the wires to have a separate GND but that was not better.
Finally, I've used a new STM32, totally separated , changed my config and bam worked without a glitch, even if it's in the same area.
I'm wondering if my 1st STM32 was just overloaded (2 coils wings (4 flippers + slingshots + drain) + switches on all remaining slots.
Anyway, it's now working as it should and stable.
Time to put some lights everywhere
One surprising thing : the led show is perfectly running in mpf monitor, however it has a different behavior in real.
as you can see in https://github.com/BENETNATH/mpf_dealers_choice I've got a attract mode lightshow that works perfectly well.

I'll do a video to explain it better.

Here is the video:

it seems it's not a white issue.
I've replaced FFFFFF by white and it's now working well.
The new issue is now when Adv_Bonus token reach >30 , all led lights go out even if the lightshow should continue..
I need to troubleshoot my code.

More progress, with help from MPF, OPP and cobra18 (thank you again!)
Yesterday, I managed to code the rules for bonus multiplier, and lights.
That was a real journey for a non-coder like me.
But now, we have a working bonus counter with leds, plus a working 1-9 rollover completion for double then triple bonus.
And we have a lightshow on attract mode, thanks to the GREAT showcreator for MPF.

Still a lot to do, and a lot of questions to ask, but that's going in the good direction!!

Now that I have a correct logic, I can make more progress and fine-tuning on the classical rules.
I made a post to clarify all rules as I made some mistakes :
https://pinside.com/pinball/forum/topic/willimas-dealer-s-choice-some-rules-questions#post-6242143

All classical rules have now been coded and tested. That's really great.

I've spent a lot of time to code a way to switch between classic and modern rules, today's commit on the github shows how I'm dealing with that and it seems to be working now. https://github.com/BENETNATH/mpf_dealers_choice
I'll now code for modern rules !