Big, glossy holes clustered at the top: underproofed. The bread ballooned in the oven instead of expanding evenly.
Small, tight crumb throughout: overproofed, or under-fermented flour, or both.
Even, medium holes with translucent walls: you nailed it. This is what most home bakers should aim for, not the giant Instagram holes.
Gummy strip near the bottom: underbaked. Bake ten minutes longer, or lower the rack.
Take a photo of every loaf you cut. Six months of crumb shots is a real baking education.