What are you keeping them in? Maybe they’re picking up this weird aftertaste from the container. That shouldn’t happen.
A lot of good bread recipes call for mashed potatoes. Make potato bread!
Make little dumplings, the same recipe you’d use for potato pancakes but simmer them in broth. Add some vegetables and you’ll have a nice soup.
Unlikely… this happens regardless of what container I’m using, and the taste is pretty consistent (and also gets more noticeable as time goes on). I’ll even notice it sometimes if I get homefries made from leftover potatoes at a greasy spoon, where they’re using entirely different equipment from what I have at home.
I know I’m weird that way. 
Most people don’t even notice the taste when I complain about it, so it’s probably something specific that I’m sensitive to (kind of like the whole cilantro love/hate thing, or the fact that my BF thinks that cheese tastes like earwax instead of delicious dairy goodness)
Hopefully, my image isn’t tarnished too badly (ha!). I’ve been cooking for over 40 years (to general acclaim), but the only restaurant venue was as a short-order cook long ago. Much of what I know has been learned from books and trial-and-error. And I have taken classes on the important things like sauces, stocks, spices, etc. Also classes on Cajun/Creole cooking and one for Indian food that taught me you really need to grow up making the stuff to get it right. Some others.
I believe that good cooking is an innate skill. Anybody can learn to do basic cookery, but the truly great chefs are using a part of the creative brain that others don’t. There are folks on this board who are, in my mind, better at this than I am, but as I said: what I do, I do very well.
Maybe they’ll make some slapdash pierogi? Heat up your mashers and add some cheese, then mash the cheese in again. Go buy some wonton wrappers from the store, use the cheesy mash as the filling, seal and boil/fry.
I’ve never done this, but it seems like it might work. Maybe. Now I need some leftover mashed potatoes.
My wife’s grandmother uses them to thicken soups as well, particularly ham and green beans, a sort-of stew here in PA Dutch country.
I always see the lady on the informercial with that grill thing that lets you make things like cake batter and hot sandwiches one at a time. She put’s mashed potatoes in there instead of bread.
I wonder if any of that works?
Would you believe we always deliberately make extra mash so we can have tuna flake one or two days later?
Mame Household Tuna Flake:
large tin canned tuna
1T chopped parsley
2T chopped onion
1T lemon juice
1t Worcestershire sauce
1T Thai or Viet fermented fish sauce
beaten egg
1 cup mashed potatoes
Mix the lot together. Season with salt and pepper. Divide into convenient sized patties - we use about a cupped handful per patty. Roll in breadcrumbs if you prefer crispy coating. Fry - oil works best for this.
FWIW, I used to be a food microbiologist. I am much less worried about food poisoning than most people, including my husband :). I even designed my current kitchen with perforated metal mesh in the pantry door so we can properly hang and age salami, but moulds on food that aren’t supposed to be there do worry me.
Mould on food.
If you have mould growing on hard cheese, like cheddar, cut off more than just the mouldy bit. Some moulds, particularly the coloured ones, can produce mycotoxins, which can diffuse through the product they are growing on. The diffusion is 3dimensional, not planar, so you should cut off at least 2 -3 cm in each direction from the EDGE of the visible mould. Not all moulds produce mycotoxins, but unless you are a mycologist it is hard to tell by looking, and those toxins can be very nasty. In the “permanent organ damage” field of nasty, not the “got the runs for a day” field. Frankly, unless the mould is both white and small, I just throw the cheese out.
Never sniff a mould - depending on the type of mould, the spores can colonise your lungs, and it ain’t a pretty outcome. Look up aspergilliosis if you are interested to know more.
My mom used to make this all the time. She’d make more potatoes tha necessary and leave some aside unseasoned to make either this cake or some INCREDIBLE doughnuts.
MASHED POTATO CAKE
2 c. sugar
1 c. sour cream
1 c. butter
1 c. mashed potatoes
1 1/2 c. black walnuts
1 1/2 c. raisins
1/2 tsp. ginger
1/2 tsp. vanilla
1/2 tsp. salt
1 tsp. baking soda
1 tsp. baking powder
2 1/2 c. flour
5 eggs, beaten separately
2 sq. unsweetened chocolate
2 tsp. cinnamon
Mix together all ingredients for 3 minutes. Bake at 350 degrees for 30 minutes.
ICING:
1 box powdered sugar
1 stick butter
2 tbsp. milk
1 tsp. vanilla
Blend together and ice cake.
If you’re not afraid of a little deep-frying, you could always turn them into croquettes. With a recipe courtesy of Paula Deen. 
ETA: Paula Deen’s recipe doesn’t even require you to go all out with a deep-fryer. But you’re certainly welcome to use one.