It's very easy to get a Guava version conflict because (a) Guava frequently adds new stuff, and (b) Guava semi-frequently deprecates and removes stuff a couple versions later.

So all you need is one dep that needs Guava version X with method M that is removed in version X+2 (say) and another dep that needs something new introduced in version X+2, and you have a Guava version conflict. That's, Guava releases are not backwards compatible due to removal of classes and methods.

You can sometimes fix this with a technology like shade or OSGi or whatever to allow private copies but it does not always work.