Production build fails after upgrade to version 12

[4nderss]

🐞 Bug report

• new
• build
• serve
• test
• e2e
• generate
• add
• update
• lint
• extract-i18n
• run
• config
• help
• version
• doc

Is this a regression?

Yes, the previous version in which this bug was not present was: 10.1.1

Description

After updating from 10.1.1 to latest version. We can no longer build our applications with the optimization flag set to true.

🔬 Minimal Reproduction

run ng build with optimization set to true

works when its set to false

🔥 Exception or Error

2021-05-21 07:49:47: webpack 5.36.2 compiled in 84034 ms (5e690d36f371e40bd6f2)
✔ ES5 bundle generation complete.
✔ Copying assets complete.
✖ Index html generation failed.
undefined:1:3650594: property missing ':'

🌍 Your Environment

Angular CLI: 12.0.1
Node: 14.15.0
Package Manager: npm 6.14.8
OS: win32 x64

Angular: 12.0.1
... animations, cli, common, compiler, compiler-cli, core
... elements, forms, language-service, platform-browser
... platform-browser-dynamic, router

Package                         Version
---------------------------------------------------------
@angular-devkit/architect       0.1200.1
@angular-devkit/build-angular   12.0.1
@angular-devkit/core            12.0.1
@angular-devkit/schematics      12.0.1
@schematics/angular             12.0.1
ng-packagr                      12.0.0
rxjs                            6.6.7
typescript                      4.2.4

Anything else relevant?

Tracing back the update steps I see that bulding works fine in 11.2.

[alan-agius4]

Duplicate of #20760

[angular-automatic-lock-bot]

This issue has been automatically locked due to inactivity.
Please file a new issue if you are encountering a similar or related problem.

Read more about our automatic conversation locking policy.

_{This action has been performed automatically by a bot.}