The layer immediately below the bark is the lifeline between the roots and the canopy. In most trees, the lines are straight so the part of the tree that doesn't do well is straight above the damaged trunk. If the tree can heal itself, the tree will slowly regrow in those areas. I don't see any signs the bark is healing. What is happening on the other side of the tree? If the bark is damaged all the way around, the tree will die.
The original damage might have been caused by frost cracks or sunscald. Both happen in winter, look the same and usually occur on the south and west sides of the trees but have different causes. Unfortunately, Japanese Maples are one of the trees affected by frost cracks and sunscald. Here is a good article from the University of Maryland.
https://extension.umd.edu/hgic...
I lost a Cherry tree to frost cracks or sunscald this year after we had snow and lower than usual temperatures in the middle of an otherwise warm fall. The tree leafed out normally and bloomed, then died, one branch at a time.
