The Organization for Security and Co-operation in Europe's press release on the 2018 Azerbaijan election would qualify:

On election day the observers reported widespread disregard for mandatory procedures, a lack of transparency, and numerous serious irregularities, including ballot box stuffing. More than half of the vote counts were assessed negatively, largely due to deliberate falsifications and an obvious disregard for procedures.

However, the OSCE's report on Turkey's 2017 constitutional referendum would not qualify, as it doesn't directly claim that manipulation of the vote count took place.

The OSCE will be observing: ODIHR opens election observation mission to Türkiye

Resolves according to their first report in which they comfortably make conclusions about the election. It doesn't count if their first report just describes their investigations, or if they explicitly say that a clear conclusion on this matter will be given in a future report.