C# – ASP.NET Core 2.0 JWT Validation fails with `Authorization failed for user: (null)` error

I'm using ASP.NET Core 2.0 application (Web API) as a JWT issuer to generate a token consumable by a mobile app. Unfortunately, this token couldn't be validated by one controller while can be validated by another (using the same validation setting within the same asp.net core 2.0 app).

So I have a token which is valid and could be decoded, has all the required claims and timestamps. But one endpoint accepts it, while another gives me 401 error and debug output:

Microsoft.AspNetCore.Authorization.DefaultAuthorizationService:Information:
Authorization failed for user: (null).

[40m[32minfo[39m[22m[49m: Microsoft.AspNetCore.Authorization.DefaultAuthorizationService[2]
      Authorization failed for user: (null).
Microsoft.AspNetCore.Authorization.DefaultAuthorizationService:Information: Authorization failed for user: (null).
[40m[32minfo[39m[22m[49m: Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker[3]
      Authorization failed for the request at filter 'Microsoft.AspNetCore.Mvc.Authorization.AuthorizeFilter'.
Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker:Information: Authorization failed for the request at filter 'Microsoft.AspNetCore.Mvc.Authorization.AuthorizeFilter'.
Microsoft.AspNetCore.Mvc.ChallengeResult:Information: Executing ChallengeResult with authentication schemes ().
[40m[32minfo[39m[22m[49m: Microsoft.AspNetCore.Mvc.ChallengeResult[1]
      Executing ChallengeResult with authentication schemes ().
[40m[32minfo[39m[22m[49m: Microsoft.AspNetCore.Authentication.JwtBearer.JwtBearerHandler[12]
      AuthenticationScheme: Bearer was challenged.
Microsoft.AspNetCore.Authentication.JwtBearer.JwtBearerHandler:Information: AuthenticationScheme: Bearer was challenged.
[40m[32minfo[39m[22m[49m: Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker[2]
      Executed action MyController.Get (WebApi) in 72.105ms
Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker:Information: Executed action MyController.Get (WebApi) in 72.105ms
Microsoft.AspNetCore.Hosting.Internal.WebHost:Information: Request finished in 271.077ms 401 
[40m[32minfo[39m[22m[49m: Microsoft.AspNetCore.Hosting.Internal.WebHost[2]
      Request finished in 271.077ms 401 

My validation setup is below:

var secretKey = Configuration["Authentication:OAuth:IssuerSigningKey"];
var signingKey = new SymmetricSecurityKey(Encoding.ASCII.GetBytes(secretKey));
var tokenValidationParameters = new TokenValidationParameters
{
   ValidateIssuerSigningKey = true,
   IssuerSigningKey = signingKey,
   ValidateIssuer = true,
   ValidIssuer = Configuration["Authentication:OAuth:Issuer"],
   ValidateAudience = true,
   ValidAudience = Configuration["Authentication:OAuth:Audience"],
   ValidateLifetime = true,
   ClockSkew = TimeSpan.Zero,
};

services.AddAuthentication(options =>
{
   options.DefaultScheme = JwtBearerDefaults.AuthenticationScheme;
   options.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
   options.DefaultChallengeScheme = JwtBearerDefaults.AuthenticationScheme;
}).AddJwtBearer(options =>
{
    options.RequireHttpsMetadata = false;
    options.TokenValidationParameters = tokenValidationParameters;
});

These two endpoints are identical, just live in different controllers, both marked with the Authorize attribute.

How is that possible?