Floating Sludge

A plant recently experience shock loading event which resulted in the MLSS having settability issue.   The sludge is constantly floating ( scums formation) in the clarifier, causing sludge to overflow into the treated water channel. Anyone has any idea what chain of events may cause the destabilisation of the mlss causing it to not settle? Any recommendations for remedy? The mlss has dropped 30% after the shock event and current sludge age looks young ( light brown colour with greyish tint). Thank you all for any feedback