likely a memory issue, I've been having the issue in ftb some and have memory of similar happening all the way back in 1.2.5 where the game would refuse to load textures once it began reaching it's limits
re logging usually fixes it though
also it might be a chunk error if it's just a giant hole
go to %appdata% delete the ftblauncher folder, get the new launcher exe, then run it where you had your old one
it tends to be weird like that sometimes, I had a similar issue with mine and that of my little brother and sister but this solved it
just pointing this out but nbt editor as last I heard corrupts modded worlds
as well as I've seen there is an issue on my current server where when mystcraft is installed if a animal walks into a nether portal the whole server crashes, that may be what you are experiencing
well there is likely two issues at play, first being server sided lag, the second being poor update coding on barrels themselves, they rarely ever accurate show how much is in them properly when interacted with by anything other than players
if it appears to be fps lag you may need to turn the sound off, minecraft is well known for it's lag filled sound system
I have a fairly good computer but I can't play with the sound on without the game freazing up due to having the sound on
if it's the server itself running slow then it...