In some versions he is one with God at all times, in other versions he's a direct link to God.

Let's go with latter version.

If he is a direct link to God, he has the answers on speed dial at all times, the only issue is the line is not always connected. That's not to say it can't be connected by the snap of a finger, but just that before said snap, there is no connection going on.

When Jesus was not omniscient, the reason was because God broke the connection, which is acceptable for his plan to work out, which is Jesus dying for our sins, then returning.

Now the main answer, is Jesus a reliable source (based on this scenario described in the description) yes, Jesus is not only a reliable source, he's the most reliable source we have. If you ask Jesus anything, he can get answers from God. If the question should be answered it will be answered, and if the question should not it will not. Plus it's not like Jesus would lie. If we ask a question (what is the meaning of life as an example) he will either tell us, God's answer, or he will tell us he does not know, which would be God cutting the connection.

Yeshua was a very good source in my most humble opinion. He died on the cross for our sins.

He is the apparent human path of God. Like a physical manifestation of God, hence the lack of sin.

Just chiming in on one particular point:

He says "my God, my God, why have you forsaken me?" In this moment he is clearly human - he is not omniscient.

TLDR:

1) If the omniscience/omnipotence of God represents an aggregate property of the Trinity rather than the capabilities of each individual aspect, Jesus' lack of informational knowledge regarding why is not inconsistent.

2) If the 'why' in question is philosophical rather than informational, the question does not make any implications insofar as omniscience is concerned.

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Details:

1) Firstly, consider the Christian concept of the Trinity. In this concept, 'God' refers to the trinity of the Father, Son, and Holy Spirit. Omniscience and Omnipotence are attributed to God- these traits may be reflected in an aggregate of the three nodes, without any individual node necessarily being itself omnipotent and omniscient.

2) Setting that aside and working under the assumption that each aspect of God is itself omnipotent and omniscience, there is still room for philosophical differences between the aspects; If one looks at the actions attributed to God in the earlier portions of the Torah/Old Testment vs. the newer portions of the Torah/Old Testament as well as the New Testament, there certainly appears to be basic philosophical differences in the attributed actions. We can already observe that two people with the same knowledge can have widely differing interpretations of said knowledge, so a philosophical 'why' uttered by Jesus on the cross isn't necessarily inconsistent with anything here.

By 'philosophical why,' I refer to the fact that many of us, under times of stress and suffering, have put forth the question of "why" when we already know the answer (or at least think we do).

Example 1: On losing ones house- Why? Failed to pay mortgage/rent due to loss of income and/or significant increase of expenses. The question is philosophical.

Example 2: On the death of a loved one- Why? Medical reasons, eg. an injury, illness, or general degradation of vital organs due to old age or another condition. The question is philosophical.