I think there is a factor of UB that makes it have a steeper learning curve than the corresponding issues in other languages: with Java a lot of that category of bad code will throw exceptions and you'll get useful stack traces. UB often results in some seemingly nonsensical runtime state (eg something being null immediately after a null check, or a null dereference only leading to a segfault later in a place that locally has no pointers).

Compare mutating a container in a way that invalidates a live iterator: in java it's a specific exception that you can read on stack overflow, and in C++ it's just a use after free that might still appear to work correctly a random percentage of the time.