While playing earth 1000AD there was an invisible unit. I believe it was a knight. Anyhow, it only happened once but just figured I should bring it up. Anyone else have similar problem?

Yeah... every now-and-then a unit will temporarily disappear. Sometimes it happens when attacking, but most of the time it is when defending. Usually after the battle, it will appear on the mapagain, but not always.

That happened to me in the American Revolution scenario with the British frigates turning invisible during their first bombardment.

Happened to me on multi today. I was sorta freaking out that I only had 1 horse archer in my unit left, but it turns out there was still two.

SP game I attacked a single Grenadier only to find there was another one hidden underneath. Thankfully it didn't impact my strategy.