The biggest sign of startup failure is lack of growth: slow sales, no new hires, no new features, etc. In general, stagnation. Development issues like redoing work, poor coding practices, etc. rarely matter unless it goes on for a long, long time.

Smaller companies are often disorganized (and is one of the reasons some folks prefer them over larger, more bureaucratic organizations), but are also more flexible and can pivot faster. If you are at a startup that won't pivot when things aren't working, that's also a big problem.