配置存储被释放

//I've also tried without this line
services.AddDbContext<ConfigurationDbContext>(options 
    => options.UseSqlServer(connectionString));

var migrationsAssembly = typeof(Startup).GetTypeInfo().Assembly.GetName().Name;
services.AddIdentityServer()
   .AddDeveloperSigningCredential()
   .AddAspNetIdentity<ApplicationUser>()
   .AddOperationalStore(options =>
   {
       options.ConfigureDbContext = builder =>
           builder.UseSqlServer(connectionString,
            s => s.MigrationsAssembly(migrationsAssembly));

        // this enables automatic token cleanup. this is optional.
        options.EnableTokenCleanup = true;
        options.TokenCleanupInterval = 30;
   })
   .AddConfigurationStore(options =>
   {
      options.ConfigureDbContext = builder =>
         builder.UseSqlServer(connectionString,
          s => s.MigrationsAssembly(migrationsAssembly));

   });

我试图从api生成一个令牌,将identityserver作为客户端使用。有时ConfigurationDbContext已经被释放,有时在第一行抛出,有时在最后一行抛出

private async Task<string> CreatePaymentsTokenAsync()
{
    // Get client for JWT
    var idpClient = await this._configurationDbContext.Clients.Include(x => x.AllowedScopes)
        .FirstOrDefaultAsync(c => c.ClientId == Config.APIServerClientId);
    // Get scopes to set in JWT
    var scopes = idpClient.AllowedScopes.Select(s => s.Scope).ToArray();
    // Use in-built Identity Server tools to issue JWT
    var token = await _identityServerTools.IssueClientJwtAsync(idpClient.ClientId, 
        idpClient.AccessTokenLifetime, scopes, new[] { "MyApi" });
    return token;
}

这段代码偶尔会工作,但大多数时候它会抛出一个错误,即上下文被处理了,你知道为什么吗?