I am facing issue thread related issue in asp.net core identity in asp.net core?

Question

Error Message :A second operation started on this context before a previous operation completed. This is usually caused by different threads using the same instance of DbContext

 public async Task<UserSearchDto> GetSingle(string userId, string baseUrl)
        {
            
            var user =await  _userManager.FindByIdAsync(userId);
            if (user != null)
            {
                UserSearchDto userSearches = new UserSearchDto
                {
                    data
                };
                return userSearches;
            }
        }

In above service FindByIdAsync throwing this exeption

while i am debugging step by step then i am not facing this error

my setup in startup file as below

services.AddTransient<IAuthService, AuthService>();

Even i changed above service method but its not working why it requires more time to perform or there is any another issue?

Edit

these manager are passed in service

 private readonly UserManager<ApplicationUser> _userManager;
 private readonly RoleManager<ApplicationRole> _roleManager;

this is ctor

public AuthService(UserManager<ApplicationUser> _userManager,
            RoleManager<ApplicationRole> _roleManager,
            IConfiguration configuration) : base(configuration)
        {
            this._userManager = _userManager;
            this._roleManager = _roleManager;
        }

User manage and role manager are used from Microsoft.AspNetCore.Identity

 services.AddDbContext<Db>(options =>
            {
                options.UseSqlServer(mySqlConnectionStr);
            }
            );

Answer 1

The DbContext has a scoped service lifetime, coupled to an asp.net request. Thus services using the context should preferably also have a scoped service lifetime.

Answer 2

I can recommend you such approach (TModel can be yours UserSearchDto):

    // Or your db context directly in class but this is better
    private readonly IServiceScopeFactory _factory;
    
    public async Task<TModel> FindByIdAsync(ulong id)
    {
         using var scope = _factory.CreateScope();
         // your context gets here
         await using var userManager = scope.ServiceProvider.GetRequiredService<UserManagerContext>();
         // this is important
         var entities = userManager.Set<TModel>().AsNoTracking();
         // data should be filled after FindByIdAsync(ulong id), not in this method
         return await entities.FirstOrDefaultAsync(t => t.Id == id);
    }