Brinsea incubators are usually quite reliable and since you've had success with that incubator in the past it's likely some fluke from shipping eggs, which can open up all kinds of opportunities for unusual issues. I'm really wracking my brain on this one but if nobody has a better solution, if the egg doesn't release enough fluid by lockdown, I would make a tiny safety hole through the shell at the air cell and pour out the fluid before placing back into the incubator. Some people put safety holes into their hatching eggs even when they don't have an issue with fluid build up so this shouldn't pose an issue. Just be sure to increase humidity as usual once the fluid is removed so it doesn't cause the membrane to dry out.