Just to be pedantic, there is no such thing as Axolotl. Olm is a new protocol, different from Signal Protocol, that uses the double ratchet internally for part of its function. However, they've made other design decisions that are different from Signal Protocol and may have received less study or scrutiny at this point.

We renamed the Axolotl Protocol and the Axolotl Ratchet because of the confusion between the two (https://whispersystems.org/blog/signal-inside-and-out/), particularly when people just used the word "Axolotl."

Often when people intentionally continue to use the word "Axolotl" now, it's because they're trying to benefit from that confusion. Olm, however, has been clear about being a different protocol.