When my industrial furnace is smelting,it guide "imcomplete multiblock".I replace the furnace block but it still guide this.Only if i dig up all machine casing block and build it in another place,it can work.But a few minutes later,it guide "imcomplete multiblock" again.
All machine casing are in the same chunk,and i load the chunk by FTBUtilities.
Modpack FTBContinuum-1.0.2-1.12.2
Forge 14.23.3.2689
Mod 2.15.6.642

I was able to reproduce this by placing a casing adjacent to the complete multiblock. not sure why it invalidates it. this doesnt occur with industrial grinder. just the industrial blast furnace.

Are you playing in single or multiplayer? Is there anything in the log (When you open / have the gui open?).

Is the machine still working even though that message is being displayed?

I can't reproduce it in Continuum 1.0.2.

I see some weird check about no tile entities below multiblock. Do you have anything there, like chests, etc?

My blast furnace already processed some galena dust and it is still valid multiblock.

I'm playing in multiplayer game,server is download from twitch too.Today i replace the 2 air block to lava,and this issue didn't happen again.I think you can try to use air inside and whether this issue happen

When the message being displayed,the machine didn't working.

I cannot re-produce this, ensure that the mutliblock is correct with no extra casing touching the outside.

there should be either air or lava inside blast furnace. This is how it works. BTW, placing lava inside furnace will give you almost free heat bonus. )

oh, thanks .... good to know! ^^

i have the same issue. after several rebuilds (in different junks) it works again for a few sec. or minutes. playing on smp server (FTBContinuum-1.4.1-1.12.2) aswell. And by the way ... i am pretty sure it has something to do with feral lanterns illuminating the inside of the blastfurnace.