I have below code which will call couple of services and finally add the items to collection. But the problem is it’s not updating my list though I am using thread safe collection ConcurrentBag class. I am using Parellel.ForEach for fast performance for processing each request id. My code is compiling with no error, and I can see the values list while debugging but at the end of request getting null in response. Also sometimes, the code is getting executed twice when I do debugging. I am not sure is it because of Parellel.ForEach loop.

public async Task<ModifiedCollection> GetUpdates(Request request)
{
    ModifiedCollection modifiedCollection = new ModifiedCollection();
    List<string> Ids = request.Ids.Distinct().ToList();

    if (Ids.Any())
    {
        Parallel.ForEach(Ids, async id =>
        {
            var globalId = "";
            var result = await _provider.GetList(id, request.IsActive);

            var baseValue = result.FirstOrDefault();

                if (baseValue?.CustId.FirstOrDefault() == Constants.ABC)
                {
                    var predicate = _provider.GetPredicate(
                                 type: baseValue.type,
                                 id: null);

                    var matter = await _provider.GetItem(request.IsActive, predicate);

                   
                    if (matter != null && matter.CustId.Contains(request.ToRequest.CustId.FirstOrDefault()))
                    {
                        result = await _provider.GetList(matter.MapId, request.IsActive);
                        globalId = id;
                    }
                }

                result = BackDraw(result, request.FromRequest.CustId.FirstOrDefault());

                Parallel.ForEach(result, async item =>
                {
                    var IsValid = true;
                    if (!String.IsNullOrEmpty(request.ToRequest.EligDate))
                        IsValid = CheckEligibility(item, Convert.ToDateTime(request.ToRequest.EligDate));

                    if (IsValid)
                    {
                        var resultMatter = await _provider.GetStructure(item);
                        var uItem = await GetUItem(resultMatter);

                        if (uItem != null)
                        {
                            if (!uItem.rNotes.IsNullOrEmpty() && !uItem.property.IsNullOrEmpty())
                            {
                                modifiedCollection.ModifiedItem.Add(new ModifiedItem
                                {
                                    Id = item.ObjectId,
                                    Version = int.Parse(item.Version),
                                                                       
                                });
                            }
                        }
                    }
                });
            
        });
    }
    return modifiedCollection;
}

Class defination is as below

public class ModifiedCollection
 {

     public ConcurrentBag<ModifiedItem> ModifiedItemBag { get; set; }
     public Updates()
     {
         UpdatesCollectionBag = new ConcurrentBag<ModifiedItem>();            
     }
 }

If I replace the Parellel.ForEach with just foreach its working but the response time its taking is 8+ secs. How can I make this code work and fast as well. I have tried to add lock as well at the time of adding item to collection but still list if not getting updated and getting null response. I need to make improvements in performance of this code. Any help would be appreciated. TIA