The molds are Accurate Molds, I did clean the cavities with hot distilled water, alcohol, and I think I also used lacquer thinner  once also. Scrubbed the vent lines also. Not sure what else to do. 
Joe S

After you have done all of that, if you still have a problem, smoke the mold. Anything will work; wooden match, candle, butane lighter.......  Candles can be tricky.  Do not contaminate the with dripping wax!

Not sure you are having this problem but I have a Saeco mold that casts the #740, 410 gr bullet that if there is the slightest breeze (I use a fan to move fresh air past my face) on the mold I get incomplete fill-out on one side of the mold. In contrast I have a Paul Jones mold where he used the same mold blocks that Saeco uses, and which casts a larger 430 gr bullet, that is not affected by the same breeze.

Also, make sure the sprue cut off plate is not too tight pressing down on the top of the mold. his can have an effect on how well the corners of the base fill out.

Run the mold too at at least 750 degrees or somewhat hotter.

I dissassemble and then soak a new mold overnight in mineral spirits.
then wipe it dry
then soak it for an hour or so in acetone.
then shake off/wipe off the acetone ( don't just let it dry)
NOw, I inspect the mold cavity with an eye loupe  for any wire edges. They can be gently removed with an Exacto knife.
Next, check for snug/but not sticky fit on the alignment pins.
Adjust carefully-gently drive pins in deeper- if any looseness.
Now adjust the sprue plate tightness so it is just snug enough to prevent it opening up "by gravity"   
Now warm it up to temp before starting casting.
Works for me for a relatively short casting breakin.
After warm-up/initial casting you may need to adjust the sprue plate tightness again- NOT tight, just snug enough....
ALSO, I do NOT oil or wd40 the mold between uses.
Molds go into a Good gasketed GI ammo can along with
several pieces of VCI rust inhibiting paper.
Ready to go next time out of the can
beltfed/arnie

I don't remember, from the other thread, what your mold is made of. I've never had problems with a iron mold but, have fought aluminium and brass, a few times.

With alum molds, I found that NEI Mold Prep, usually sloved the problem. It's made of fine graphite, I think.

The most trouble that I had was with a NOE, 2 cav, brass mold. I was aniuos to see what the bullets measured so, I cast it w/o doing anything to it, not even taking the oil out of it, figuring to would burn out and be ok.

I threw hundreds of bullets back in the pot, with that mold. I put mold prep on it, boiled it, sprayed it with cleaning spray.

What I finally did, was start all over. Got the mold prep off with alcohol, I then used my regualar method. I use hot water, with dish soap with Boraxo added, then plain Boraxo. Dried it and cast. It was better, I then heat cycled it on the electric shove, 2 or 3 times and it finally started casting good bullets. I still get about 5 out of 100 that have wrinkles but, I figure that's good with a 2 cav.

As JB says, make sure the ladle spout contacts the sprue plate, when casting. You'll keep a better temp in side the mold that way and the pressure it provides, helps fill out.

Nothing more frustrating than not getting good bullets!!!

Frank

Indeed,
keep the dipper spout on the sprue plate for a few "moments",but do not press hard. Let the dipper/lead's
own weight keep it onthe sprue plate.
This is just so you don't seal the sprue plate to the top of mold blocks thereby reducing venting
beltfed/arnie

Joe - may work for you  but it works for me ...
* with the ladle spout on the sprue plate while pouring, tilt the spout just a tad (spout still in the sprue hole).  What you will see during the pour is the melt bubbling out on the side of the spout = escaping air in the mold = more melt fulling the blocks.  And remember to press the plate down when cutting the sprue = better base bottoms with a clean cut

Finally,  I have cleaned my molds with a free sample of 
Micro -90 for close to 10 years now.  The sample is concentrate and you wash the molds with a 2% solution.  So it lasts a long time. I use distilled water from the dehumidifier
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When ask for the free sample - identify that you have a  gunsmith business.  They don't ship to just a Joe Blow

When you get all your casting fine tuned - how about a couple of bullet pictures