From Forums:
Heya, quick question. I've been fiddling around with Zero-boiloff tanks lately and as much as I try, on highest warp levels it still boils off although there is enough EC and genration. Or is Zero-boiloff not exactly zero over a long time?

I can provide you with 2 craft files, all tanks are configured as ZBO and LiquidHydrogen config.
One works as intended, the other one has boil off at highest warp rate although all requirements are met to maintain zbo. Since the single tank is working fine I still think the flaw might be in design / configuring on my side but if so it should also drain on the second highest level, which it doesn't.

https://www.dropbox.com/s/e633rweptcud7i3/Boiloff%20Yes.craft?dl=1

https://www.dropbox.com/s/e633rweptcud7i3/Boiloff%20Yes.craft?dl=1

I wish the designs would be similar, but maybe they help identifying the issue (if there is one, I still might have made a mistake, maybe you can tell me).

I can duplicate your experiences with the craft you provided; at max timewarp it does experience boiloff.

I have found that the cause of it in this case is the minimal EC charge available on the craft -- you only have the 600ec provided by the command module. If you add a few k more worth of EC the boiloff-at-max-warp will stop.

The root cause of this is down to how KSP integrates resource updates at high timewarp rates, as one big chunk without any substeps (as far as I know). This limits the EC-delta available at any update to the max of the vessel, even if it would have produced/consumed more than that amount during that update period.

I may be able to solve this by switching to a 'best guess' mode at higher timewarp rates, using the last-known state of if there was enough EC generation; this is what I currently use for out-of-focus catch-up and it seems to work well enough.