Hi! Modules periodically disappear again, fact. This is a real problem. You need to seriously check what's the matter. Every time clean cache... its not good.
Here's another person noticed this:
https://www.joomlart.com/forums/d/34177-modules-disappear
Specially as evidence i show page with bug. Visit this page .../o-proekte
There must be footer at the bottom position, but it dissappeared. Then try to clean the t4 framework cache. A footer will appear and views correctly, but only for a while, then appears randomly over and over again, on different pages.
P.s. Before that, you can clear the browser cache to make sure that the browser has nothing to do with it.