C# – Nhibernate unexpected row count rising after deletes

Problem:

I'm getting error:

Batch update returned unexpected row count from update; actual row
count: 0; expected: 1

when some entity is deleted between fetch and delete. After any next delete row count and expected are rising for e.g.:

Batch update returned unexpected row count from update; actual row
count: 11; expected: 12

Code:

var queueEntry = _session.Query<MyTable>().FirstOrDefault(x => x.Id == id);
if (queueEntry != null)
{
    _session.Delete(queueEntry);

    try
    {
        _session.Flush();
    }
    catch (Exception ex)
    {
        _session.Clear();
    }

    return 1;
}

Attempts:

I've tried few things with no success, I've added this lines in catch clause:

_session.Disconnect();
_session.Reconnect();

I've tried to wrap whole code I've putted here with transaction and instead of _session.Flush() I putted transaction.Commit().

Mappings:

This is mapping by code

public class MyTable : IEntity
{
    public virtual int Id { get; protected set; }
    public virtual string Type { get; set; }
    public virtual string Source { get; set; }
    public virtual string OperationType { get; set; }
    public virtual bool IsVisible { get; set; }
    public virtual DateTime? Timestamp { get; set; }
    public virtual string ContentId { get; set; }
    public virtual int Priority { get; set; }
}

Question:

Is there any way to reset this expected value, so I can continue removing values without exceptions?

Of course entities are removed from table, but I keep getting exceptions. Using empty catch clause for ignoring this exceptions is not a solution for me.

EDIT:

Addtional info: this table is queue for long running process, it has no child tables, just few things usefull for service. Posted mappings. It happens after some time, not after first delete.