Hi AdrienG,
It's typically not Octane's "fault".
I must emphasize on double-checking the mesh itself.
The rule of thumb in rendering (and some other domains) is: G.I.G.O.
Have you rendered in Standalone by exporting an Alembic?
I'd suggest doing so and reporting back.
If possible, sharing the problematic mesh so OTOY devs (or some members) can inspect.