After closing the Angular Material Expansion Panel via a boolean variable,
it closes just fine but to reopen it again you will need to click it 3 times to reopen it.
Apparently in Angular 6 it works just fine with the identical example but i obviously don’t want to downgrade, i tried Angular 10 & 11 and it didn’t work.
I Also tried to close it via different ways like the panel’s close method etc but no difference.
Source: Angular Questions