That its for sure. Sometimes outside sources will cause an upgrade to fail
outright. That is because the dependencies can get out of whack and the
upgrade will attempt to shut off outside sources and upgrade base packages
before it can upgrade the distribution. I have encountered failure more
often than not.
The party line from Canonical is that upgrades are safe.and work. I notice
that Mint which is based on Ubuntu does not encourage upgrading distros.

People who have had success likely have it because they use plain vanilla
Ubuntu while mine its severely modified. That being said upgrading through
two versions really complicates things and there is much room for error. It
could work but it is a question of how much time and effort one is willing
to spend.