Read the symptoms before you touch anything
When a flowsheet misbehaves, resist randomly changing values. First read the evidence: Does it converge at all? How fast does the residual fall? Which messages appear? A loop that crawls toward convergence often signals a near-runaway recycle (purge too small); a loop that diverges often signals an infeasible spec.
Diagnosis first, then a single deliberate change, then re-run.
Diagnose from the monitor and messages first; change one thing at a time.