I knew a potter who made his living with b-mix cone 10- for about 20 years. He worked about 12 tons a year during this period.It is really prone to cracking and he fought large forms cracking for many years until he went out of business ( from other issues)
I use about 500 #s of B-mix over about a 5-7 year period-mostly for large vases and super tall pots (market is really slow for them now)
I am a porcelain production potter mostly now (except for salt pots)
I gave up large flat forms with it in the 80's-
I suggest only using it for smaller work which you have zero trouble with-why fight it?
B-mix dries super uneven (lips) so you need to even it out.
Bad batches come and go with all clay makers and I doubt thats the issue-Can you tell from the numbers on boxes to see if there are several different batches involved?? You can call John Pacinni at laguna west with the box numbers if you really want to know about bad batches. Many potters do not pay attention to these box numbers ( or even seee them) but they are the only tracking you can do. I know which ton I'm on by them and which is the oldest clay in shed by them to use it 1st.
When you buy in many tons at a time you learn that the numbers make sense in even tons and old to newer clay as the numbers increase.
This body has always been a cracker on large flat forms-platters-baking dishes etc--common stuff for us in the business-Try a better body witch can hold up to flat stuff stress.
I use a body from Laguna for flat slab work called Half and half WC382 cone 10. it can be streched pulled twisted and handled with no cracking-its half Daves porcelain and half WSO bullet prove-I do not throw it.They sell two kinds on this. one is finer tighter with sand if I recall or finer grog?. I use the WC 382 almost like a porcelain body with a little grog
The most invincible clay I know is wso-its more like some non clay thing but it cannot be foiled by large flat or uneven drying-I do not like my glazes on it so thats my main issue with it as well. If I wanted to say make a 3x2 foot fish for the wall I use this WSO and have with zero issues.
I do not fire midrange so cone 6 users will have to add some of thier bodies to this list-life is short and crappy cracking issues is something you should not fight with as we old timers have moved thru it in our past. Try a new body