Same issue here since 22nd June. My Reynor was 59 levels and now become 5 levels, Asia server .
Actually I review some threads, and it happened in last year from Feb to July and in May this year. Unfortunately there was not officially resolution for the issue, while tech support only collected people who presented the issue.
This is level drop off thread in last year: [Main Thread] - Commander Levels Reset
And in May this year: Lvl co-op commanders bug