png, tiff type frames disappear in nested sequences (cc 2017 12.0.0)

Hi! I've been struggling this for many many hours now. I am building an animation of tif and png files. So far it's been going more or less ok on Premiere.

Now I have a series of tiff or png files (I tried both types). Thy appear properly in the preview when they are on the timeline as individual clips. But when I nest them so that I can animate them, every second clip disappears from the preview. The first one show and then the second doesn't. The order makes no logic, sometimes the first shows, and then the second. on its own the nested sequence shows, but if other images are beneath or on top, the same thing happens. It is extremely annoying, I have tried everything, re-saving the files, saving on other formats etc. All of them are rgb files. Do you have similar problems, or do you have some solution?

Thank you!