Either one of these should get what you need:
Get-ADSyncRunProfileResult
Get-ADSyncRunStepResult
For Example:
- Identify the run setup you want to investigate the error
Get-ADSyncRunStepResult -RunHistoryId 9f78e5b4-4d35-401f-9a7b-491dcfa2a19f - Check the sync errors occurred in that run step
(Get-ADSyncRunStepResult -RunHistoryId 9f78e5b4-4d35-401f-9a7b-491dcfa2a19f).SyncErrors | Format-List