I have the same issue. Is there any solution about the problem.

Yes, inside the snippet I also have no issues. I have to mention that I use react and mdbootstrap within a symfony installation which used used together with webpack and encore. But this does not explain why the button increases within the simple home.js component.

Home.js

import React from "react";

import { MDBBtn } from 'mdb-react-ui-kit';

function Home(props) {

return (
    <>
     <MDBBtn>Speichern</MDBBtn>
    </>
)
}

export default Home;

package.json

{
"devDependencies": {
    "@babel/preset-react": "^7.14.5",
    "@symfony/stimulus-bridge": "^2.0.0",
    "@symfony/webpack-encore": "^1.0.0",
    "axios": "^0.21.1",
    "core-js": "^3.0.0",
    "mdb-react-ui-kit": "git+https://oauth2:@git.mdbootstrap.com/mdb/react/mdb5/prd/mdb5-react-ui-kit-pro-essential",
    "prop-types": "^15.7.2",
    "react": "^17.0.2",
    "react-dom": "^17.0.2",
    "regenerator-runtime": "^0.13.2",
    "stimulus": "^2.0.0",
    "webpack-notifier": "^1.6.0"
},
"license": "UNLICENSED",
"private": true,
"scripts": {
    "dev-server": "encore dev-server",
    "dev": "encore dev",
    "watch": "encore dev --watch",
    "build": "encore production --progress"
},
"dependencies": {
    "@babel/plugin-proposal-class-properties": "^7.14.5",
    "@babel/plugin-transform-runtime": "^7.15.0",
    "dotenv-webpack": "^7.0.3",
    "react-csv-reader": "^3.3.1",
    "react-router-dom": "^5.2.0"
}
}

webpack.config.js

const Encore = require('@symfony/webpack-encore');
if (!Encore.isRuntimeEnvironmentConfigured()) {
    Encore.configureRuntimeEnvironment(process.env.NODE_ENV || 'dev');
}
const Dotenv = require('dotenv-webpack');
Encore
// directory where compiled assets will be stored
.setOutputPath('public/build/')
// public path used by the web server to access the output path
.setPublicPath('/build')
// only needed for CDN's or sub-directory deploy
//.setManifestKeyPrefix('build/')

/*
 * ENTRY CONFIG
 *
 * Each entry will result in one JavaScript file (e.g. app.js)
 * and one CSS file (e.g. app.css) if your JavaScript imports CSS.
 */
.addEntry('app', './assets/app.js')

// enables the Symfony UX Stimulus bridge (used in assets/bootstrap.js)
.enableStimulusBridge('./assets/controllers.json')

// When enabled, Webpack "splits" your files into smaller pieces for greater optimization.
.splitEntryChunks()

// will require an extra script tag for runtime.js
// but, you probably want this, unless you're building a single-page app
.enableSingleRuntimeChunk()

/*
 * FEATURE CONFIG
 *
 * Enable & configure other features below. For a full
 * list of features, see:
 * https://symfony.com/doc/current/frontend.html#adding-more-features
 */
.cleanupOutputBeforeBuild()
.enableBuildNotifications()
.enableSourceMaps(!Encore.isProduction())
// enables hashed filenames (e.g. app.abc123.css)
.enableVersioning(Encore.isProduction())

.configureBabel((config) => {
    config.plugins.push('@babel/plugin-proposal-class-properties');
})

// enables @babel/preset-env polyfills
.configureBabelPresetEnv((config) => {
    config.useBuiltIns = 'usage';
    config.corejs = 3;
})

// enables Sass/SCSS support
//.enableSassLoader()

// uncomment if you use TypeScript
//.enableTypeScriptLoader()

// uncomment if you use React
.enableReactPreset()

// uncomment to get integrity="..." attributes on your script & link tags
// requires WebpackEncoreBundle 1.4 or higher
//.enableIntegrityHashes(Encore.isProduction())

// uncomment if you're having problems with a jQuery plugin
//.autoProvidejQuery();

module.exports = Encore.getWebpackConfig();