Process Author Email Notification Issue

We are moving away from the legacy workflow due to its coming deprecation next year. We were playing around with Process Author to replicate all our existing workflows. However we can't seem to get it to work consistently. I would say its success rate is only about 30 to 40% of the time.

We implemented even the simplest email notification workflow for this just to explore how it works. What's strange is that we noticed a warning icon when previewing the completed processes.

Does anyone know what this icon is for? Would appreciate if you can share your expertise on this.

Thanks,