Multiple tilesets.json as one tileset

Hello, is there any way to add multiple tilesets to primitives?
Cesium version is 1.70
Currently we have like 4 big tilesets. We try to add them like:

var tilesets = ["/tileset2,json", “tileset2.json”, etc]
tilesets forEach(element => {
tileset = viewer.scene.primitives.add(new Cesium.Cesium3DTileset({
url: element.url)}

When we open our site, we have randomly getting errors like A 2D tile failed to load
Error: Invalid tile content.

When we add only one of these tilesets, all work fine.
Trying make one tileset.json pointing to other tilesets but same issue.
Problem is when we want to add couple od them. Sometimes we get 3 working, sometimes only one.