My front loader erupted like a foam party and lived to tell the tale

I did almost the same thing with my old Maytag top loader a few years back. My wife bought one of those concentrated 2x bottles and I didn't read the label, just filled the cap like I always had with the regular stuff. About halfway through the cycle the whole drum turned into a foam party and suds started creeping up over the rim. I caught it before it hit the floor, luckily, but I still lost an hour of my evening scooping bubbles out with a plastic cup like I was bailing a boat. What worked for me besides the empty rinse cycles was tossing in about half a cup of white vinegar during the second rinse. It seemed to knock the suds down fast. I've used that trick a couple times since when the soap gets away from me.

One thing I'd say is keep an eye on the drain for a few loads after. Mine drained slow for about a week afterward and I'm pretty sure there was leftover soap sludge sitting in the hose. Ran a couple of hot cycles with barely any detergent and it cleared up on its own. And yeah, the dried flakes behind and under the machine are the worst. I was sweeping little crunchy soap bits out of that corner for weeks.

Funny reading this because I had the reverse problem for years. After reading horror stories online I got so paranoid about oversudsing that I was using maybe a teaspoon of detergent per load in my LG front loader. Clothes started smelling musty after a few months and I couldn't figure out why. Turns out underdosing lets grime and body oils build up on the drum and in the gasket, and that's what actualy causes the smell people blame on the machine. The repair guy who came out said most front loaders only need a tablespoon or so of regular HE detergent for a normal load, and less than that if you have soft water. He also told me the suds lock thing happens way faster with soft water because there's less mineral content to knock the foam down. We're on city water here and it's pretty soft, so my tablespoon is really more like three quarters of one.

For the dried flakes behind the machine, don't just wipe. Pull the machine out and vacuum back there first, otherwise you'll smear it around forever. And run a hot empty cycle once a month, it keeps the residue from building up in the drain pump area where you can't reach. One thing I'd keep an eye on is that door boot. If suds got forced into the folds, mold can set up shop in there pretty quick. Wipe it dry after every load and leave the door cracked open.

The spot that caught me out after my own oversudsing incident was the inside of the door gasket, not the visible fold you naturally wipe but the channel underneath where suds pool and dry into a gluey film. Run a finger around the whole groove a few days later and you will likely find more residue than you expect, and that is exactly where musty smells get thier start if you leave it. Mine had a chalky ring at the lowest point of the fold that took a couple of passes with a damp cloth to shift. You can also check wether your machine has a drain pump filter behind the little access panel at the bottom front, since a soap-heavy cycle can leave scum there too, though the manual will tell you if yours even has one.