I live at 4160 elevation, so I decreased the yeast by 1/4 tsp in the Mary Lunn bread recipe. The dough rose up to the window of the bread machine 2" from the top of the bread pan. The top looked like a sponge, the dough went down the sides of the bucket, and it was hard to remove all the bread from the bread maker. I cut the top 2" off in order to find the handle then had to still gently dig to get the handle up to remove the pan. I followed the recipe exactly, except for the yeast decreased by 1/4 tsp The bread baked in the tub perfectly great color, baked 4 hr 20 mins to get that color, normal time would be 4 hr and 10 min for lighter color. Not giving up, please help~
I couldn't say what exactly caused it, but yeast is a living organism, and recipes are based around average rising times and rising volumes. It could have been a fluke, or it could be that something in your particular combination of parameters is prone to cause this result regularly.
Luckily, you don't need to know the actual cause. You can just scale down the ingredients to make a smaller batch. Continue making half or 2/3 of the recipe to find out if it regularly fills your machine, and if yes, use that amount for a loaf. If it starts making very small loaves, it must have been a one-off event, and you could return to using more ingredients at a time.
Also, consider switching to weight measurements. Volumentric measurements are notorious for being very imprecise in baking, so they are much more likely to produce unwanted results.