With red oak the growth rings are open and porous. Roy Underhill, on one of his shows, place one end of a three foot length in a bucket of water and blew through the other end; no problem making bubbles in the bucket. Your problem is probably combined factors. Cut only six weeks ago it probably held as much water as it could (compared to cutting in the winter) and the open pores allowed the water to just flow out.
Reaction wood is much more susceptible to cracking. Almost any limb wood is reaction (either tension or compression), that is why almost no lumber mill with touch it.
The picture I attached is pecan limb which my SIL sent up to me from south Georgia and it had been cut about two weeks prior. The pith is at the pin and I cut the log from about 1:00 to 7:00. It did not give equal size pieces by a long shot but it did make it much more stable. A lot of time I leave wood in long sections but the pecan I cut and removed the pith. If you cut the logs to the length you mentioned, which is fine, I would suggest you also go ahead and make a cut through the pith so the wood can shrink back on itself.
I agree with Wildwood that in your pictures I do not see any indication of sealer. Wildwood, do you use melted paraffin or something similar? I do have some cracks that sill appear with anchorseal but have never had the sealer peel away from the wood.
They who can give up essential liberty to obtain a little temporary safety, deserve neither liberty nor safety. Benjamin Franklin