I'm not sure about which console your referring to, but I did some tests in the last days using the latest default standard neogeo plugin cores available in pack v12 (I am calling them "standard of this pack" I'm not sure the exact version of them, and I will tell another option that I find the best for my case) and I got some problems with both cores:
Hexaeco standard core gave memory dump on about 5 games from 7 tested.
The dump shows always after unibios screen, exactly when neo geo logo animarion is starting:
It also gave green screen on Mslug3 for a while and went to a black screen, but didn't freeze, you can press home, see the menu and exit. It's really weird behavior, because I tested some games with this same plug-in some days ago and all worked, I even had set this one up as default plug-in to show the games.
Retroarch standard core loaded some games but gave error of no cache file found (image). I think there's something wrong or maybe it's looking for the cache files on a new place. Some games loaded, but the buttons doesn't work, so you can walk but can't shoot or jump.
In other hand, I created a new plugin configuration in wiiflow and "inserted" an older core on it,
it's neo geo 1.7.5/1.7.6 VM (I used magic number 12345678, lol). I just tested Mslug 1,2,3,4,5,X, garou, last blade 2, RBFF and they all worked today with this core. It's that one that load the crom with a green progress bar. I already have the cache files for the bigger games created in romcnv and stored in more than one folder (I just don't remember where they are, but could look for them and copy to new place, if it's needed for newer cores to work). One bad thing using this core is that, when exiting the game it freezes on wiiflow logo and need to hard reset the wii.