Weird artifacts with WMTS map tiles

I’m working on some code which can move map tiles (created from geo-tiff), and I’m getting some weird visual effect.
I don’t know if this is a bug in the CesiumJS engine, or I’m doing something wrong.
Any help would be appreciated.

Here’s the sandcastle example:

The effect I’m referring to is that when you zoom in, stripes of transparency appear on the imagery layer. When zooming out, the stripes go away.
I can’t understand what 's causing them.

stripes

Is this a bug?
Should I be opening an issue on the CesiumJS repo about this?

Hi @Adrian_Onsen,

Thanks for the report! I can reproduce and have opened an issue for you on GitHub.