It sounds like this is about CPU-PPU clock alignment. There are 4 possible alignments every Famicom and NES could end up with at each boot. If you have a PPU that has this bug and speckles appears in a game you need to boot it into another alignment that works with that game by power cycling it until it works.
Soft reset will not work (not sure if any games even have this). Hard reset might work on a front-loading NES. For a Famicom and a top-loading NES you might need to power cycle since the reset button doesn't reset the PPU on those.
1/4 chances sounds about right, so it's probably this. I guess the root of the problem is on the NESRGB side, though it would be great if a workaround can be introduced on the N8 side, for example by forcing the bug-free CPU-PPU alignment that corresponds to the N8 cart. Maybe KRIKzz can discover if this or another workaround if possible once he gets a NESRGB kit to test.
I don't know for sure, but I don't think it's possible to do force clock alignment using a flashcart. The Hi Def NES can do it probably because it's adding all kinds of stuff to the hardware. It probably has to be fixed on the NESRGB.
It sounds like technically the bug is in the PPU, so its not really a fault of the NESRGB or the EverDrive N8. The NESRGB could probably select a specific clock alignment/phase from the four available, but apparently different games respond better to different alignments, and some games cant be fixed at all, so I dont think locking the NESRGB into one specific alignment would really help. Its likely easier to just power the system on/off until you get the desired clock alignment (The reset button will also work on some systems, but not all of them since Nintendo changed the reset circuitry between revisions and some models dont reset both the CPU and PPU when using the reset button)
I think the only solution really is to either get a console with a Rev.H PPU (Later models of AV Famicom, and perhaps later NES toploaders as well) which apparently fixed the issue, or patch each game to disable writes to the PPU_CTRL $2000 register:-
https://krikzz.com/forum/index.php?topic=6221.msg48455#msg48455I would love to know if this is an option that could be added to the EverDrive N8 - a system wide "Disable writes to $2000 register" - or if this sort of patch would be too complicated and will always require game specific patching.
What I find interesting is that I think this PPU clock alignment bug seems to also affect the stock Composite video output as well:-
http://krikzz.com/forum/index.php?topic=9549.msg72393#msg72393So the bug doesn't just affect the PPU EXT data that the NESRGB / Hi-Def NES use.
Finally it should be noted that there are some completely unrelated issues which can cause similar problems with flickering pixels/speckles:-
-A number of NES games have flickering pixels near the edge of the screen which was expected to be cut off in the overscan area of a CRT TV, but is visible when using a flat panel TV or scaler (Same applies for many retro systems) this is completely normal.
-There are some game specific bugs that cause similar issues, such as the flickering line in Super Mario Bros 3 just above the status bar:-
https://wiki.nesdev.com/w/index.php/Game_bugs-The NESRGB and Hi-Def NES can have similar issues if you leave the Q1 composite video transistor on the motherboard:-
https://www.youtube.com/watch?v=e0cRXP9Du5M-Finally, if you use a power supply that is poor quality/underpowered (Or evening a failing original PSU) this can also apparently cause similar issues.
