I think you already have your answer, but let me elaborate a bit.
The places in the middle where the filament is missing - those places are either dirty or too high.
The area in the back where the filament is sticking, but isn’t filling the area correctly, those areas are too low.
Most likely cause for both is the build plate on an Ender just isn’t perfectly flat. You can try to adjust it to get it closer to being level. But I’ve always found I’ll have sections that just aren’t right. And so, I just don’t print on those sections. Find the areas that do print well, and locate your prints there.
Last note - try putting down a layer of painter’s tape. I find that helps tremendously with both of the points you’re fighting.
I think you already have your answer, but let me elaborate a bit.
The places in the middle where the filament is missing - those places are either dirty or too high.
The area in the back where the filament is sticking, but isn’t filling the area correctly, those areas are too low.
Most likely cause for both is the build plate on an Ender just isn’t perfectly flat. You can try to adjust it to get it closer to being level. But I’ve always found I’ll have sections that just aren’t right. And so, I just don’t print on those sections. Find the areas that do print well, and locate your prints there.
Last note - try putting down a layer of painter’s tape. I find that helps tremendously with both of the points you’re fighting.