Error in HTML not reported on file open

[mickaelistria]

Using @angular/language-server 0.1001.0 and @angular/language-service 10.1.1, I see a regression compared to @angular/language-server 0.1000.4.
To reproduce, with Eclipse WIld Web Developer

1. open and provision (npm install) a simple project like https://github.com/eclipse/wildwebdeveloper/tree/master/org.eclipse.wildwebdeveloper.tests/testProjects/angular-app
2. Open appComponentWithHtml.ts , let tsserver and angular-ls load (ie show outline or provide some Angular specific completion)
3. Then open appConponentWithHtml.html
   EXPECTED: Error marker shows on incorrect template
   GOT: No error marker. Note that if I then make any change to the document, the expected error marker shows up.

With previous versions of @angular/language-server, this was working as expected, the marker/diagnostic was showing up on file open.

[mickaelistria]

Actually, the issue doesn't come from migration to newer @angular/language-serv*, but from simultaneous migration from typescript 3.9.7 to typescript 4.0.2. If using typescript 3.9.7, all @angular/language-serv* versions mentioned earlier works perfectly; if using typescript 4.0.2, all @angular/language-serv* versions mentioned earlier fail at showing diagnostic on .html file opening (but do show it after edit).

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