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This can happen if a cold snap occurred before your tree completed the process of dropping its leaves. Trees go through an active process of drawing back nutrients from their leaves and then causing the leaves to drop (known as abscission). If cold temperatures killed the cells involved in the process before the leaves fell, the leaves might stay on the tree all winter. Fortunately, this shouldn't hurt the tree, unless it happened multiple winters in a row.

This is likely a Jelly Fungus.
Here are some links with more information.
Many times it is completely harmless and grows due to wet conditions.

https://extension.psu.edu/pests/plant-diseases/all-fact-sheets/hazard-trees
https://www.gardeningknowhow.com/ornamental/fungus-lichen/jelly-fungi-on-trees.htm

Sunscald can cause peeling bark on maple trees. This article will help you:
https://ask.extension.org/questions/235796

Squirrels can also strip bark off trees. Another possibility is a disease. Check the tree for any of the disease symptoms discussed here:
https://www.gardeningknowhow.com/ornamental/trees/maple/maple-tree-bark-disease.htm

Another possibility is Verticillium wilt, a serious disease, but this would cause other symptoms as described here:
http://www.extension.umn.edu/garden/yard-garden/trees-shrubs/verticillium-wilt/

Each spring can bring different timing of leaf out. Check the neighborhood, are you seeing other trees in your area leafing out yet? Hardwoods take longer to leaf out in most growing zones.

Be patient and if you are concerned about the health of the tree you can test a few branches. Live branches bend, dead branches snap off.
You an also scratch a bit of bark. This article will help you with this test.
https://www.gardeningknowhow.com/ornamental/trees/tgen/tree-scratch-test.htm

Yes, you are correct; the seed from a Sugar Maple Tree need a cold stratification period.
This link will help you.
http://www.wildflower.org/expert/show.php?id=1917

Many variegated plants will gradually revert to a fully green form if you don't prune them carefully. The variegated parts of the plant are weaker and slower-growing than the green parts, because they don't have as much chlorophyll. This article explains more:
https://www.gardeningknowhow.com/plant-problems/environmental/variegated-plant-problems.htm

The best way to prevent this is to prune out all the green areas regularly. If you don't, they will eventually take over the entire tree.