Science
Lots of stuff in the scriptures and things that prophets have said in talks (which I was taught in the church to consider as scripture) are not supported by science. This is not a Mormon-specific problem, but it’s still definitely a problem in the LDS church. For instance, Noah’s flood in the Bible just does not make sense as a literal event. Also, the D&C states that the Fall of Adam occurred 7,000 years ago and that there was no death prior to that event. That also makes no sense scientifically.
“To cling to faith in these areas, where the overwhelming evidence is against it, is willful ignorance, not spiritual dedication.”
Want more detail? See https://read.cesletter.org/science/, https://www.ldsdiscussions.com/biblical-scholarship and http://www.mormonthink.com/scienceweb.htm