Adding ModifiedAt throws RealmInvalidTransactionException

Question

I am writing a simple WPF app that uses Realm Database.

Each time a database record is changed, I want to update its ModifiedAt property, but somehow it keeps throwing this error:

Realms.Exceptions.RealmInvalidTransactionException: 'Cannot modify managed objects outside of a write transaction.'

Here is my code where I subscribe to listen to changes and update that property. The exception is thrown inside foreach loop.

  public DreamRepository(Realm realmInstance) : base(realmInstance)
        {
            _realmInstance = realmInstance;

            _realmInstance.All<DreamEntity>().SubscribeForNotifications((sender, changes, error) =>
            {
                foreach (var dream in sender)
                {
                    dream.ModifiedAt = DateTime.Now;
                }
            });
        }

I tried to debug it, this code is triggered after most of operations get completed because of asynchrony, so I am guessing maybe the instance gets disposed by the time when it's triggered, but I don't know how to really check that.

It works pretty well in Console App but not in a WPF app.