Just a bit of play in order see the problem clearly.
The webix-jet TypeScript code is included in the project directly to make it easier to debug.
Dealing with nested subviews, and later with bundled subviews.
Branch b1 is a simple case. Works great.
Branch b2 is similar to master, but the level2 subview is loaded when an item is selected from a list.
Branch b3 moves the level1 and level2 subviews in to a module. The module is bundled into level1 webpack chunk.
With webix-jet as is, loading of level2 subview fails.
Modified webix-jet works.
There is probably a more elegant way to solve this.
The solution assumes that bundled chunks will go into a folder called modules. It works by enabling the JetApp::loadView to make a decision about where to require the page from.