Welcome to the EPUB "standard."
The only meaningful answers come from each vendor, assuming they can be bothered to answer beyond whatever cryptic, outdated boilerplate is on their help page.
The solution - quite seriously- is to stay with one or two major vendors. You won't sell enough through the third and fifth and twentieth to make any of the effort worthwhile.
ETA, addendum now that I'm on a real keyboard. I think it's a waste of time to try and place books with all of the EPUB sellers. Everyone has a success story on one or the other, but frankly, it's not like you're placing it with Target and Walmart and Macys; more like Amazon/Walmart and a bunch of niche/boutique places. Amazon covers the world and is easy to publish and manage. If you absolutely must have a second, direct-EPUB outlet, SmashWords is probably closest in convenience and reach, unless you want to target the Apple crowd specifically with Apple Books. But both of those is a waste, and slogging down the list of Kobo and others is even more so.
Point of evidence: I think I've sold three books on SmashWords, in five or six years. I sell more directly from my publishing website, which only has a storefront because I set one up 20 years ago. I've never sold anything on B&N, and never any ebooks on Ingram.
Just not worth the headache and hassle and annoyance to scrape sales from the corners of the market. Anyone who won't buy from Amazon almost certainly does their primary shopping on SW or Apple, with a sharply descending curve on the others. Duplication is pointless.
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