WordPress plugin conflicts driving me nuts

• okay, i'm desperate here. a client's main production site just totally broke after a wordpress update, and their freaking out.

• i've spent hours debugging and it's definitely plugin conflicts. i've tried deactivating one by one, but it's not clear which combination is causing the issues.

• whats the quickest, most reliable way to figure out and resolve these plugin conflicts without taking the whole site offline for days?

anyone faced this before?