I have noticed on several occasions that when attacking a planet often a second attack on a planet does not always deal damage.

The population will remain the same but I get XP for the hit and it reports the normal (-20).
I am not sure if it matter but I normally notice when doing the Secure Surrounding Space, but that is normally when I am looking at the pop so it may be irrelevant.
I am also dealing max (20) damage not sure if that matters either.
I have also noticed that as far as I can tell it always seems to be the second attack that is not registered but the first and third onward seem to be fine.

Below are images of 3 back to back attacks on a planet with a few second between hits for screen caps.

If I'm not mistaken, this is an old bug.

Currently, there are 2 which affected by this bug :
Shield
Population.

Both regenerates over time, and can exceed the maximum.

This can be replicated easily. Use a shield restorer, then shield amplifier. Your shield will still be fully replenished (should be only half-full). As long as there is no 'refresh tick', this should work (refresh tick refers to when you attack, get attacked, regenerate shield, or energy)

I've seen the exact same thing just about every time I attack a planet too NM. The second hit does not actually reduce the pop. Very annoying when using tenebris probes for legion mission.

This is one of those inconsequential glitches that have been around since the start.

Oh and Carhart, if your able to do the Tenebris probe task, that extra bit of wasted energy shouldn't be bothersome.

The energy is not bothersome. Watching the glitch in action is..... annoying. The energy might be inconsequential for you and me but possibly meaningful for noobs with very low energy bars invading a planet.

If said noob is so low on energy that 5 more breaks them, they shouldn't be trying in the first place.

The Forum is called Issues and Support. This is an issue. Your opinion on whether it matters or not or whether it should be fixed or not is irrelevant. Let Dan decide if he's going to do something about it.

all you have to do to 'resolve' this issue is to use a flux probe on the planet before your first attack. the population gets synced and every hit counts from then on.

Dan has acknowledged this 'issue' (I mean it's five energy!) in a previous thread and said it can't be fixed.

Didn't know that. I'll give it a try. Thanks for the info Senator!