With subclasses approaching and looking for reasons to play DK primary class, I decided to test this set once again on PTS... turns out it is still broken.
Like detailed in this thread from last year (that I didn't want to necro):
https://forums.elderscrollsonline.com/en/discussion/658689/basalt-blooded-warrior-molten-stance-not-working-as-intended
...basically refreshing the Molten Stance bugs out the Major Heroism buff where you no longer gain any ultimate from Major Heroism until the buff runs out. Needless to say, this is pretty annoying to deal with and would be nice to have a fix for it.
Just one Cinder Storm cast for Molten Stance, Major Heroism (not sure why cmx calls it "Base Regeneration", but you can see the double ulti gen ticks here) working correctly:

Recasting Cinder Storm after casting it once (before the Molten Stance ran out):

As you can see, we're only getting the normal ultimate ticks (sometimes 4 ultimate because of Decisive trait) & nothing from Major Heroism on the second screenshot.