Here they discuss some undesirable effects: https://www.researchgate.net/publication/254994729_Analysis_of_Pump-Turbine_S_Instability_and_Reverse_Waterhammer_Incidents_in_Hydropower_Systems
Article Analysis of Pump-Turbine S Instability and Reverse Waterhamm...
Reverse water hammer can be highly problematic and destructive and has been the cause of many failures and accidents. It can cause systems to fail and can great huge hydraulic loads on the turbo machines, equipment and connected systems. In summary, it deserves great respect!