Strange session variable behavior on multiple Ajax requests?

Question

JavaScript

Hello.

I've run into a problem that I don't know how to resolve.

I won't post the code yet. First, I will describe the problem in the general case.

There is a static class manager. With which grid view works. This class has a property that works with the session. This session is needed to store the entries selected by the checkbox in the grid view. There is some two-step functionality and that's where you need to remember the session. When a one-time check / uncheck is made, an Ajax request goes to some record and the method of adding / deleting a value in the session is triggered, and then everything is OK (the collection is stored in the session). But if you click on the checkbox five or ten times in a row and generate a lot of consecutive Ajax requests, then the session will have either zero or some one (most often the first) value (if several checkboxes are selected). I can't understand why this is happening. It is also impossible to debug in the debug in the studio, since the debug catches the first Ajax request and works with it, the rest of the requests do not get there.

Maybe someone came across something similar. Please help, friends.

UPDATE:

Friends. I've localized the problem, but still haven't figured out what the problem is.

I bring the code.
Variable names are shortened so as not to give exact code, but the logic is completely preserved. I think it will be clear.

There is this code

protected void btnAction_Click(object sender, ImageClickEventArgs e)
{
      var trs = MlEManager.MlEItems.OfType<tcT>();
      CreateSCtion(trs, userId, date, comment, sCenterId);
}

Then there is this code, already in another assembly.

public static SomeType CreateSCtion(IEnumerable<tcT> trs, Guid userId, DateTime date, string comment, Guid? sCenterId = null)
        {
            var result = SomeType.GetInstance();
            //try
            //{
                var firstT = trs.First();

                var trsCountTemp = trs.Count();
            
                var ction = new tcCtion
                {
                    UId = userId,
                    CtionBeginTime = date,
                    CtionEndTime = date,
                    CtionId = firstT.LocId,
                    SProviderAddressId = sCenterId,
                    STypeId = SType.All[SType.SAdjustment].STypeId
                };
                CManager.CContext.Ctions.AddObject(ction);
                ction.FId = ction.Loc.FId;

                if (ction.SProviderAddressId.HasValue)
                    ction.Com = ction.SCenter.Com;

                StringBuilder sb = new StringBuilder();
                foreach (var t in trs)
                {
                    CManager.CContext.CtedTrs.AddObject(new CtedT { Ction = ction, TId = t.TId, VirtualMMPlier = 1 });
                    sb.AppendLine(t.Id + "||||||||");
                }


                if (!String.IsNullOrEmpty(comment))
                    CManager.CContext.tcCtionCnts.AddObject(new CtionComment
                    {
                        Ction = ction,
                        Date = DateTime.Now,
                        UserId = CManager.CUser.UserId,
                        CtionCommentTypeEnum = 1,
                        CtionCommentText = comment
                    });

                CManager.CContext.SaveChanges();
                result.Data = ction;
        
                throw new Exception("top=" + trsCountTemp.ToString() + "========" + sb.ToString() + "======== bottom=" + trs.Count().ToString());
                
        //}
            //catch (Exception exc)
            //{
                //result.AddError(exc.Message);
            //}
            return result;
        }

If you do all of the above actions, then the exception will record that top=1 and bottom=3 (3 is the actual number of active checkboxes at the moment). Well, there will be one iteration in sb. How can it be that one trs variable in one block of code shows different data at the top and bottom?