When train engines get replaced by MUTC (https://mods.factorio.com/mod/MultipleUnitTrainControl?from=search), the window to access equipment grids no longer pops up. Looking in the Factoriopedia, they lack equipment grids at all.

Update: Specifically only with Electric Trains (https://mods.factorio.com/mod/electric-trains?from=search) it seems (although possibly other mods too).

Hm, looking at the code for those mods, it seems like a problem on either the MUTC end or the Electric Trains end (though more likely MUTC).

I can only control what happens during the loading phase (which is, creating the equipment grids for each of the train types). MUTC's effects apply during runtime (which is, replacing trains when the map is actually loaded).

MUTC has some kind of code in place to handle equipment grids, but it even has a comment stating: "TODO: UPDATE FOR QUALITY", which makes me believe that it is unfinished in some way. Trains with grids aren't exactly standard, and they might not have done any testing with this mod, so it's possible that's where the incompatibility lies.

Alternatively, MUTC just has to mark this mod as an optional dependency, which will then force this one to load first, so they can do whatever copying needs to be done during the loading phase (since they apparently do something there too). Then again, almost all of the grids are created and applied by my mod during the data phase, one of the earliest parts of the loading phase, so it's unlikely that load order is the cause of the issue.