It doesn't. One can't be omniscient and not know something, I think the problem is that people conflate Jesus and the Father as one God or being. That is a logical contradiction. Jesus wasn't omniscient. He indicated so Himself as you point out.
That is a question we will we ALL soon have answered. It mostly leaves us humans in a quandary to reconcile the two but we must remember that God is Holy and also Omnipotent . Being Prophane , there simply are many things that we can't or shouldn't try to explain and ,I think this is one of them.
By all evidence, God was the father of Jesus..how is that possible? How is God father of himself.
I think that Jesus acted as a son when He said, " If you have seen me, you have seen the Father ".
It is said that many human sons are just like their human Fathers ...No one was probably more Father and Son like these two and, why doesn't anyone mention the Mother.
Wouldn't you think that Jesus was 1/2 God and the other half Mary?..Seems logical for a Carnal Mind..God Himself said He was Spirit...I don't know, maybe Jesus was God Spiritually and Human Physically!
All I know is the Bible says that Jesus cried out during his last breath.." My God, my God....Why have you forsaken me?
To defeat Satin, did God back away from Jesus, so a fully Man could pay the penalty?
Not sure but the Bible also tells me , at the end, when God has Glorified me, I will know Him as well as He knows me..
How is that possible? I don't know but the Bible says it...maybe I won't ask Him any questions..probably He will ask ALL the questions!