The first time always works. Or production mode works also:

$ npx webpack --mode development 
[hardsource:e5a41f90] Using 16 MB of disk space.
[hardsource:e5a41f90] Writing new cache e5a41f90...
[hardsource:e5a41f90] Tracking node dependencies with: package-lock.json.
Hash: ad43ff0996a034b3aa39
Version: webpack 4.46.0
Time: 1855ms
Built at: 03/07/2021 4:58:18 pm
                Asset       Size  Chunks             Chunk Names
       ../css/app.css    197 KiB     app  [emitted]  app
       ../favicon.ico   1.23 KiB          [emitted]  
../images/phoenix.png   13.6 KiB          [emitted]  
        ../robots.txt  198 bytes          [emitted]  
               app.js   1.01 MiB     app  [emitted]  app
Entrypoint app = ../css/app.css app.js
[0] multi ./js/app.js 28 bytes {app} [built]
[../deps/phoenix/priv/static/phoenix.js] 38.9 KiB {app} [built]
[../deps/phoenix_html/priv/static/phoenix_html.js] 2.21 KiB {app} [built]
[../deps/phoenix_live_view/priv/static/phoenix_live_view.js] 113 KiB {app} [built]
[./css/app.scss] 50 bytes {app} [built]
[./js/app.js] 2.14 KiB {app} [built]
[./node_modules/@popperjs/core/lib/createPopper.js] 9.78 KiB {app} [built]
[./node_modules/@popperjs/core/lib/enums.js] 1.3 KiB {app} [built]
[./node_modules/@popperjs/core/lib/index.js] 443 bytes {app} [built]
[./node_modules/@popperjs/core/lib/modifiers/index.js] 502 bytes {app} [built]
[./node_modules/@popperjs/core/lib/popper-lite.js] 603 bytes {app} [built]
[./node_modules/bootstrap/dist/js/bootstrap.esm.js] 136 KiB {app} [built]
[./node_modules/nprogress/nprogress.js] 11.3 KiB {app} [built]
[?af33] css ./node_modules/css-loader/dist/cjs.js!./node_modules/nprogress/nprogress.css 1.42 KiB {app}
[?c85f] css ./node_modules/css-loader/dist/cjs.js!./node_modules/sass-loader/dist/cjs.js!./css/app.scss 195 KiB {app}
    + 53 hidden modules
Child mini-css-extract-plugin node_modules/css-loader/dist/cjs.js!node_modules/sass-loader/dist/cjs.js!css/app.scss:
    Entrypoint mini-css-extract-plugin = *
    [./node_modules/css-loader/dist/cjs.js!./node_modules/nprogress/nprogress.css] 4.14 KiB {mini-css-extract-plugin} [built]
    [./node_modules/css-loader/dist/cjs.js!./node_modules/sass-loader/dist/cjs.js!./css/app.scss] 521 KiB {mini-css-extract-plugin} [built]
    [./node_modules/css-loader/dist/runtime/api.js] 1.57 KiB {mini-css-extract-plugin} [built]
    [./node_modules/css-loader/dist/runtime/cssWithMappingToString.js] 2.22 KiB {mini-css-extract-plugin} [built]

But the 2nd time fails:

$ npx webpack --mode development
[hardsource:e5a41f90] Using 22 MB of disk space.
[hardsource:e5a41f90] Tracking node dependencies with: package-lock.json.
[hardsource:e5a41f90] Reading from cache e5a41f90...
internal/crypto/hash.js:84
    throw new ERR_INVALID_ARG_TYPE(
    ^

TypeError [ERR_INVALID_ARG_TYPE]: The "data" argument must be of type string or an instance of Buffer, TypedArray, or DataView. Received an instance of Object
    at Hash.update (internal/crypto/hash.js:84:11)
    at BulkUpdateDecorator.update (/home/brian/tree/personal/pm/penguin_memories/assets/node_modules/webpack/lib/util/createHash.js:61:14)
    at CssModule._computeHash (/home/brian/tree/personal/pm/penguin_memories/assets/node_modules/mini-css-extract-plugin/dist/index.js:145:14)
    at CssModule.build (/home/brian/tree/personal/pm/penguin_memories/assets/node_modules/mini-css-extract-plugin/dist/index.js:136:22)
    at Compilation.buildModule (/home/brian/tree/personal/pm/penguin_memories/assets/node_modules/webpack/lib/Compilation.js:739:10)
    at /home/brian/tree/personal/pm/penguin_memories/assets/node_modules/webpack/lib/Compilation.js:981:14
    at CssModuleFactory.create (/home/brian/tree/personal/pm/penguin_memories/assets/node_modules/mini-css-extract-plugin/dist/index.js:408:11)
    at /home/brian/tree/personal/pm/penguin_memories/assets/node_modules/webpack/lib/Compilation.js:897:14
    at Semaphore.acquire (/home/brian/tree/personal/pm/penguin_memories/assets/node_modules/webpack/lib/util/Semaphore.js:29:4)
    at asyncLib.forEach.err.stack (/home/brian/tree/personal/pm/penguin_memories/assets/node_modules/webpack/lib/Compilation.js:895:15)
    at arrayEach (/home/brian/tree/personal/pm/penguin_memories/assets/node_modules/neo-async/async.js:2405:9)
    at Object.each (/home/brian/tree/personal/pm/penguin_memories/assets/node_modules/neo-async/async.js:2846:9)
    at Compilation.addModuleDependencies (/home/brian/tree/personal/pm/penguin_memories/assets/node_modules/webpack/lib/Compilation.js:873:12)
    at Compilation.processModuleDependencies (/home/brian/tree/personal/pm/penguin_memories/assets/node_modules/webpack/lib/Compilation.js:843:8)
    at afterBuild (/home/brian/tree/personal/pm/penguin_memories/assets/node_modules/webpack/lib/Compilation.js:954:15)
    at processTicksAndRejections (internal/process/task_queues.js:75:11) {
  code: 'ERR_INVALID_ARG_TYPE'
}

How do I resolve? The only solution I have found so far is to downgrade to mini-css-extract-plugin@1.2.1 which just works, everytime. But looking through the changelog for version 1.3.0 I see nothing that would explain this.

I have this exact same problem on all my Pheonix live view applications.

Google showed me a number of hits for this error, but so far, none have actually helped.

Any ideas?