Coverlet doesnt calculate code coverage for tests until another test is added

[ReneKochITTitans]

we have 700 tests in our solution and we use the latest .net and latest coverlet.

3 test files in 1 (out of 30) test solutions are not calculated correctly:

But the tests are executed:

The mysterious thing is, that as soon as I copy the files into another solution, where already 10 more tests are executed, they will be seen:

Even no of the other files touching the EmailService.

It feels like a very wierd bug in coverlet.

A few more insight and what I tried already:

• it is the sae on my computer as another devs as in a pipeline
• downgrading coverlet or another packages doesnt help
• the 2 solutions are exactly the same and have nearly the same csproj etc.
• When I delete all files from the solution I copied the test into, the remeining tests of the emailService will not be seen again. Means, only when other tests are present it works.
• the tests itself are very boring, creating a service, calling a db, reading from it, Assert.Multiple + Assert.That and finished.

Example test:

´´´ [Test]
[AutoData]
public void ApplyDesignTemplate_ValidInput_TemplateWithoutBodyUnchanged(
DesignTemplateLogicService service,
TranslationData data)
{
// Arrange
string designTemplate = "This is a template without the body replacement token.";

        // Act
        var result = service.ApplyDesignTemplate(designTemplate, data);

        // Assert
        Assert.That(result, Is.EqualTo(designTemplate));
    }´´´

Json Output stand alone:

Json Output with in touch of other tests:

Any ideas?