According to Material-ui changelog, it should be solve in V5, which is still in alpha.
It seems that at least in some cases this issue cause by createMuiTheme. You can solve this issue by using the experimental (unstable) theme creator
If you want to get the experimental theme creator instead of removing React.StrictMode, you can change it’s import from:
import { createMuiTheme } from '@material-ui/core';
To
import { unstable_createMuiStrictModeTheme as createMuiTheme } from '@material-ui/core';
UPDATE
V5 is officially out (and now called MUI). If upgrading is an option for you – it should solve this issue as well.