Wanted to make certain of a few things before I put this all out there - but from what I have heard, the issues seem to be based in the money invested towards brand new costumes (different from the builds for Hollywood and Japan) that pretty instantly started having maintenance and performer health-related problems.
There have allegedly been many attempted fixes to make these new costumes work, and each had similar breakdowns and resulted in consistently bad performing conditions. Mario, Luigi, and Peach are far from a vacation to portray at Epic, but at the very least, they can go out for short periods and allow the performers enough ability to effectively act as directed. Toad and DK specifically were incredibly difficult, cumbersome, and prone to malfunction.
You can see the different builds just by comparing USJ DK and USH Toad, to Epic DK and Toad below.
USJ DK VS Epic DK ... the differences here are very obvious. The costume is very heavy.
The changes seem to be made in an effort to make a more expressive and animated character than USJ's DK model, including a less bulky body plan, smaller head with wider eyes, and a more clear "thumbs up" hand mold.
Notice Epic DK's non-primary arm resting on the costume leg for support, rather than being posed or at his side. That's heavy in practice. Performers have to conserve energy where they can when working with characters like Donkey Kong.
USH Toad VS Epic Toad 1 & 2 ... These differences are a lot more subtle, but look closely and you can find many.
Shape of the cap, size of the red dots, the height of his chest, the dimensions of his vest and face, and the way his pants are affixed to his body.
USH Toad is far more maneuverable and AFAIK less prone to malfunction. Epic Toad is considerably more 'squat'. Anyone I've heard work with them at EU has described them as "difficult", to say the least.
There continue to be active efforts to bring back these character M&G experiences, but it seems like the more time spent trying to fix these busted pieces, the more time these characters will be MIA for Epic Universe guests. I hope to see them return very soon.