I am growing BV2 cells in two different countries from different original stocks but exactly the same medium type and recipe, and the same flasks. In one country the cells do as expected, within 24 hours they're adhering and looking perfectly perky. In the other country 24 hours doesn't seem to be enough for them to adhere, they take up to two or three days sometimes and even then will only adhere to PLO coated flasks, which I've never had to use with this line before. I have absolutely no idea what's going wrong with these cells since I appear to be doing exactly the same in both countries! My only thought is that they're from different stocks BUT I have seen the badly behaved ones grow previously...just not recently!