Because ZingBot works in your real XING account, XING’s limits apply. XING caps the number of connection requests and the general action rate per account.
So when a workflow slows down or pauses, that is usually exactly what is happening: XING is throttling the account. This is expected XING behaviour, not a ZingBot bug. The workflow continues within those limits.
We deliberately quote no specific numbers — XING sets them, they differ per account, and they change. Anyone promising you a fixed ceiling is guessing.