To bring this issue up again.
It started to happen on our mainbase on a pvp server. Two advanced cauldrons including their content plus thralls have gone missing. They have been there yesterday night after raid time - so they clearly vanished on restart.
Edit:
I think both (or all) times it happened to stuff which were placed on triangle foundations.
Because both me and my clanmate recall it that way - both now and back when I first started this thread.
Straight ahead in the corner and between those two cauldrons have been cauldrons.
(I think I should loot them completely prior to next restart. 
)
@Funcom_Community
Would one of you be so kind to tell me if that issue being related to triangle foundations is known? (I know, I might need to wait until august.)
Ah, also reportet in current live: