When a symbol is not aligned to pixel grid, the origin is not aligned to an intersection of the grid. Thus it becomes very difficult to create pixel perfect symbols. Paths that are snapped to the pixel grid are then redisplayed offsetting from the origin, causing bleeding in the isolation mode.
This makes symbols essentially unusable as it becomes impossible to align objects scaled down to look good at the pixel level because such objects do not have easy to work with dimensions. With original objects it’s somewhat reasonable to correctly align them numerically.
There is absolutely no reason I can think of why this should be the case and it renders using symbols virtually impossible. This is a bug unless there is a setting to fix it. Essentially the pixel grid is not aligned to the ruler.
You’re asking for auto-distributed symbols that are pixel accurate? I’m not sure why a haphazard approach would result in perfect pixel alignment.
Align to pixel grid might help, if the symbols are built correctly from the start. I’ve never tried, to be honest. I have used patterns with correct pixel alignment without any trouble. You just have to take the care to build them right at the start (which is rarely simple).
If you’re looking for objects that are uniformly distributed, have you tried the Transform effect? It enables you to reposition the original or duplicate effects based on multiple transformation types. I’ve used this most often when building comps but it comes in handy within individual objects as well. Here’s a quick video overview, if you’re not familiar with the idea.