I posted this in reports before seeing this thread but might be relevant so I copy below.
---
I don't think this is a grief but may be a bug with FTBU causing items to go missing.
Yesterday I was in the middle of creating 7 ultimate hybrid solar panels, I had almost everything I needed including 7 advanced solar panels and most of the materials to convert them.
I needed some more glowstone dust and so I placed my important items into my ME storage system as I was going to the nether. So I go to the nether and I am there for about ten mins mining glowstone, I warp back to base and when I look for the advanced solar panels I had recently created they are nowhere to be found, or a lot of the materials I had been collecting to convert them.
Now I am pretty sure that no one came and stole them and this is not actually the first time something like this has happened, (Although I blamed backup restores for previous times) but this time I was on the server all the time and there was only a short time between having the items in my inventory and them being gone.
I looked up the following in google "items lost in ME storage" and found a thread discussing missing items (
https://github.com/nallar/TickThreading/issues/246) and blaming TickThreading mods for causing it which I believe is used on the server.
Can any other players confirm items going missing strangely? I think it is worth investigating in case TickThreading is causing problems.