And perfectly suited for this topic, if you don't believe what me + Hitch have been saying, have a listen to a managing editor from Houghton Mifflin Harcourt:
"Building Ebooks that Last" from ebookcraft 2019
She lists all the stats on why books get rejected (typos, formatting errors, link rot), she mentions things to avoid (Fixed Layout, dropcaps), she mentions needing to support edge cases like the Kindle 1st generation...
... and guess what, she also answers how not to get books returned:
KISS!!!