If you’ve been following along, I have been trying to understand why Solid Performance and Query Monitor don’t play well together. I contacted John Billion, developer of Query Monitor, and asked if he could do some testing to see what he discovers.
John narrowed it down to this line of code in Solid Performance which prevents the Query Monitor menu from displaying. The main culprit is the priority level for that line of code prevents the code in Query Monitor from running. It’s essentially a battle between plugins. John recommends that the team behind Solid Performance increase the priority level from 1 to 10 for that action.
This dev note in GitHub contains more details. While John plans on implementing client side rendering which will nullify the issue, it’s a ways off. Until a fix is implemented, don’t be surprised if these two plugins don’t work well together on your setup.