Notice: Some players are experiencing missing dimension items, keys and ownership issues. Trion have not yet responded and the 3.3 Known Issues Thread doesn’t have this issue listed yet.
For now, it’s probably best not to enter your dimensions or move anything around whilst Trion finds a fix.
[Update 11:43AM PDT] – Carpy has posted that your dimensions are a-okay, they were just not loading properly.
A fix is coming and your dimensions are still alright, they were just not loading properly.
Sorry about that.
[Source: Carpy]
[Update 11:51AM PDT] – The fix will require downtime. No ETA. [r]
RiftGrate 
All issues are caused by Arak.
This will likely be a hard one to track down since it isn’t effecting everyone. I checked several of mine this morning as well of that of a guild mates. Nothing was missing. I didn’t do anything to them last night after the patch. Possibly the ones with missing items did? Or else it’s an extremely random bug.
According to Trion some of them just weren’t loading properly. Luckily nothing bad will happen – everything is still there. Requires some shard downtime to fix though.