G800 Captain reported the FMS was displaying inconsistent and mismatched data after a new runway was entered and the flight crew became high on the arrival profile while troubleshooting the issue.

Narrative

We were descending into ZZZ on an IFR arrival when ATC issued a runway change. After inputting the new runway into the FMS; the system displayed inconsistencies and failed to synchronize with the active flight plan. We attempted several times to correct the issue; but the FMS continued to show mismatched data. During this troubleshooting; we became high on the arrival profile. Recognizing the situation; we advised ATC of the FMS issue. ATC responded promptly by issuing a heading and altitude to help us re-establish a stable descent. The remainder of the approach was uneventful. This FMS synchronization problem is a known software issue in the Gulfstream G800 and is expected to be resolved in future updates. No safety compromise occurred; but workload increased significantly during a critical phase of flight. Factors: Runway change late in descent; known FMS software bug causing sync failure; increased crew workload during troubleshooting. Reported issue to ATC; followed ATC vectors and altitude instructions; completed approach safely. Recommendation: Expedite software update to address FMS sync issue.