Can only update a mounted or mounting component (Submit).

[DeividasBakanas]

Submit component is rendered out of the form before form is mounted. If Submit component is unmounted before Form is mounted error is raised.

Error reproduction: https://codesandbox.io/s/yjq0mm6m11

Click Toggle submit, then Toggle form and you'll get the error.

[DovydasNavickas]

Done: https://github.com/SimplrJS/react-forms/commit/513172f9e11471e88bb93e002a8fd1163d1fd697 (with a temporary setTimeout in one place, so I'm not closing the issue)