I can't remove the liquid from the blast furnace, even though there is steel in it

why

Having the same issue. Latest 1.20.1 version.

It seems like the block entity is not updating the contents on the server side but just on the client side (anymore, it worked for a long time and then just randomly broke). You can see the timer ticking down and liquid being produced in the HUD, but if you relog, the furnace is set back to 0 liquid and the items are back. If you break the block it dropt both iron and limesand, but not the coke dust.

After some testing I have found the issue, its the hot air. My coke oven ran out of coal and didn't supply hot air anymore. The client side thinks the furnace can work without it, the server side does not. You get the viual of the countdown and so on, but nothing is happening on the server.

Note that this can also be used to craete buggy visuals in general if you resupply the hot air, as client and server now both have a working furnace, but the countdown and item/liquid counts don't match.