I normally do not print on them either, but I have one customer that loves to send them. I've repeatedly told them not to send those, but they still do.
I don't have any bleed blocker(other than the Digital ELT underbase black from OneStroke). I really don't want to buy it for a contract job of 140 pieces when this is the only shirt we struggle with.
I think Gildan designed that fabric to be as hard to print as possible.