Image thumbnail on Android client

Good morning mates,
I am running NC server 15.0.2 and Android client 3.4.2
everything works fine but I have some problem with caching the image thumbnails on Android Client.
I have a “images” folder of 4GB (but also tested with a folder of 100MB) and pictures thumbnail creation is very slow.
Tried to refreshing by swiping down does not work.
Works only if I force to close the app, but after re-opening it creates no more than 8 picture thumbnail…