Similar to another post I read, this exercise fails even if I view the solution and copy/paste into my answer and submit. I see the following errors in my log file.

1880 | 16:29:21: Boot Camp: Looks like you aren't allocating securities and liquidating appropriately...
1881 | 16:29:22: Boot Camp: Exercise failed. Please try again..

This is the key event handler for security changes.

public override void OnSecuritiesChanged(SecurityChanges changes)
        {
            _changes = changes;
            Log($"OnSecuritiesChanged({UtcTime}):: {changes}");
            
            foreach (var security in changes.RemovedSecurities)
            {
                if (security.Invested)
                {
                    Liquidate(security.Symbol);
                }
            }
            
            //2. Now that we have more leverage, set the allocation to set the allocation to 18% each instead of 10%
            foreach (var security in changes.AddedSecurities)
            {
                SetHoldings(security.Symbol, 0.18m);
            }
        }