Constant NROS_RMW_RET_AMBIGUOUS_BACKEND 

pub const NROS_RMW_RET_AMBIGUOUS_BACKEND: NrosRmwRet = -16;

Phase 128.A.3 — more than one backend is linked and no NROS_RMW=<name> selector was supplied. Caller must either set the env var or use Executor::open_multi.