Which sealant are you using?
The Wheel Milk that I'm currently using has recently let me down on a number of occasions.
Even in-and-out thorns have left me with sealant spurting out all over the place. I've had to get off the bike and rotate the wheel so that the puncture is pointing downwards and also have had to let air out of the valve before the sealant stops pouring out. I've then had to wait for about 5 mins before re-inflating.
I never had this problem when using Joe's.
So it's back to Joe's for me.
Cheers