Sub-synchronous oscillations are a major concern within the GB transmission system. Specifically in central and southern Scotland, where minimal synchronous generation remains on the network, several complex oscillations have been detected. Likely due to the connection of a significant number of inverter-based resources. This paper presents the work in detecting, analysing and mitigating a sub-synchronous oscillation problem that affected the system for a decade which was solved in March 2026 by employing a collaborative, non-fault approach between the involved parties. ScottishPower Transmission’s expansive wide-area monitoring system was utilised to gather event data, before dissipating energy functions were applied to track the oscillation energy path. Phasor measurement units correctly identified the participants, but the deployment of waveform monitoring identified complex, higher frequency, coupled, positive and negative sequence components indicating an event with significant unbalance. Live system tests were conducted to assess the impact of the greatest participant which showed the oscillation removed from the system when the device disconnected. Saturation of a single phase was detected demonstrating the effectiveness of the complex oscillation tracking performed with the waveform monitoring units. Remedial action was taken and participation in the mode was not observed when the device returned to service.