It appears that in a recent updates to either type definitions in my project, or some library, that a few of my timeouts and intervals might be causing issues:

ERROR in [at-loader] ./src/pages/ExamplePage.tsx:41:23
    TS2345: Argument of type '{ intervalId: Timer; }' is not assignable to parameter of type 'Pick<IState, "intervalId">'.
  Types of property 'intervalId' are incompatible.
    Type 'Timer' is not assignable to type 'number'.

After a little digging, I was able to find that using window.setTimout or window.setInterval should return the correct type of number – it looks like NodeJS uses Timer.

Hope this helps!