I was summoning Neos Knight using using Neos and Aqua Dolphin, but Neos did not gain any attack from at all from it. According to the card, it should gain "half the attack of the warrior monster (not named Neos) used to summon it". So in this case, it should've gained 300 attack but it didn't.
Am I missing something here, or is this a potential bug with the card?
Did you use Neos Fusion to summon it? Neos Knight's effect only activates if it is fusion summoned - Neos Fusion counts as a special summon rather than a fusion summon, so won't activate Neos Knight's attack boost.