Used on a non-mockito object error in Mockito

I'm getting this error

Used on a non-mockito object
package:test_api                                     fail
package:mockito/src/mock.dart 929:7                  _makeVerify.<fn>
test/delegates/tryarg/void/delegate_test.dart 38:13  main.<fn>.<fn>

running my test, I don't believe my

mixin ErrorHandler {
  void call(Object e, StackTrace s);
}

import 'package:mockito/mockito.dart';
import '<the `ErrorHandler` path>';

class MockErrorHandler extends Mock implements ErrorHandler {}

void main() {
  group('something', () {
    final _errorHandler = MockErrorHandler();
    /// more not relevant stuff
    test('something', () {
      /// more not relevant stuff
      when(_errorHandler.call(any, any)).thenAnswer((_) {});
      /// more not relevant stuff
      clearInteractions(_errorHandler);
      /// more not relevant stuff
      verify(_errorHandler.call(any, any));
      verifyNoMoreInteractions(_errorHandler);
    });
 });
}

I don't want to bore you with my lengthy test, but just showing you that _errorHandleris in fact a Mock and the call seems to reach in fact the errorHandler in the class

Can you help me understand this error