Erratic corn germination

I’ve been planting sweetcorn in succession since early May. Every time I do it, I only get about 60-80% germination.

But instead of having seeds here and there that don’t come up, it seems like it’s five or six in a row, almost as if there something environmental going on. Any idea why?`

Soil, water, pests, … Can you provide a picture?

I have them covered with netting now. Keeps the critters off that were stealing plants, but still have some that just never germinate.

I’ll get a pic later. Thing is it seems to happen no matter what the weather conditions are at the time. Dry, wet, anything in between.

What do the ungerminated seeds look like?

I did a very small sweet corn planting in a 4’x8’ raised bed this year. It is on a slight slope and the back 18" gets water logged. No seeds germinated in that area, the rest of the seeds did fine. Could be a coincedence but I’ll probably try to avoid that in the future.