Which @angular/* package(s) are the source of the bug?

compiler-cli, compiler

Is this a regression?

Yes

Description

At our company we use @angular with custom cdn.
This means we make @angular js bundles with webpack and use externals.
The angular cli project is hooked to @angular-builders/custom-webpack
We also have @My-company custom angular libraries (ng-packagr) which also render a js bundel in a custom cdn. These use compilation mode partial.
This work perfectly up until @angular 20.0.x.
So the problems i encountered:

• some elements not renderer well and causing other elements not to be renders
• issue with viewchild
• issues with mat buttons in mat dialogs

I could isolate the problem to @angular/compiler and/or @angular/compiler-cli (both versions need to be the same). I did this by gradually updating each package to 21.1.

If we use compilation mode full in the @My-company libraries then it works. But I can't just move to this system as we also have third party libraries which are partially compiled.

When I read the documentation there seems to be something new in the compiler regarding 'optimized template compilation'. So my guess the problem is related to this area.

Probably some elements are jitted but something doesnt work out and is being skipped?

It's a critical problem because we have 50+ applications running with this architecture (externals and cdn-like bundles. We wouldn't like to lock on 20.0.x.

Please provide a link to a minimal reproduction of the bug

No response

Please provide the exception or error you saw

Please provide the environment you discovered this bug in (run ng version)

Anything else?

No response