Sent two air attacks, one with 5 level 1 bombers, the other with 5 level 1 fighters and 5 level 1 bombers. This is what happened:
You'll notice that both attacks resulted in no infrastructure being destroyed. I've experienced this before, but I'd like some clarification of what is actually happening here? Is this a mere chance outcome of a bombing run, or is it actually a bug?

This happens to me a lot when I use lvl 1 bombers

I've done this with 5 x lvl 2 Bombers and frequently done no damage. I think it depends how much infra the person has. Although, I'm sure one day one attack did nothing and the second attack took 6 infra or something like that, which doesn't make any sense at all.

I frequently do 0 damage when my opponent is less than 200 infra. With low bombing strength, the damage is also very random. I've done 0 followed by 17 infra before. You were attacking someone with ~200 infra with only 5 bomber strength. Neither part of this will result in high damage, if any. You probably shouldn't even bother with a large airforce until you get level 2 or 3s. Even if you get bombed a lot, you're gonna see most of the time.

I forgot to mention one thing. In comparison to bombing runs, cruise missiles are almost unaffected by your opponents infra. I've never been able to actually ZI someone with bombers, but always defeat alerts and cruise missiles. Don't know if it is even possible for a bomber to bring someone to 0 infra.