I'm trying to build a custom set of column blocks using InnerBlocks and am having trouble passing attributes to block templates. To start, I scaffolded a new plugin using

The code editor shows that your attributes are being passed and being saved.

If you are still encountering an issue, double check that you are clearing your browser cache before retesting and also check the browser console to see if any errors are present.

As you mentioned you have already reviewed the Gutenberg code for Columns/Column, a tip would be to look at how they do variations for creating the options in your Inspector Control. Hope this gets you back on track with creating your block.