Column widths wildly inconsistent

Maybe I’m the only one having this problem but

When I use Stackable’s Columns Block, I ask for three even columns and it shows them that way in the edit page. But as soon as I publish, the widths of the columns go caflooey with no apparent logic.

I was beating my head against the wall trying to solve it and thought: does vanilla WP columns block do this? So copied and pasted content to test.

Am I missing something about how to keep widths consistent?

I don’t really need a fix as the fix I found works: DO NOT use Stackable’s Columns. But if there’s an easy fix (or I’m an idiot, which is possible) please let me know.

THANKS,

Jim

The page I need help with: [log in to see the link]