I’ve read that before. I have no idea why or how to fix it…

Looks great. My only issue is with the two batmobiles. Maybe try to make the center any other color than black, maybe Grey like a road color, so they pop out but make the outer border black to fit the motif.

No expert, but maybe look into foundation patch, for where I am, it’s a rubberized sheet that would glue to the outside around the affected area. Once back filled, the pressure from the dirt is more than enough to keep it in place. I have done that kind of repair before, and it worked for years after till the place was sold. As repairs go, it’s inexpensive. You just need a shovel time and the patch. Just do your homework as to it being a viable solution for a block foundation as mine was poured, but I don’t see why it wouldn’t work. As was said before, trying to fix it from the inside is an uphill battle.