Fix:

Preferences → Tools → Spring-loaded Tool Shortcuts

«[…] change the Timing Sensitivity from 200 to 675 miliseconds and you should be good to go.»

That is called spring-loaded tool, it allows you to temporarily switch to a given tool, use it, and return to the previous tool. For instance: you use the brush tool, then hold Z, click to zoom, release the Z key and you get the Brush tool you had before. You need to click quickly to switch tool permanently.