I'd first try to contact the FEVE department within RENFE:

https://www.renfe.com/es/en/ayuda/contactar-renfe-feve

If they don't see any error, then contact customer service.

OK, just for completeness -- I have continued this discussion in the German railway enthusiast Forum “Drehscheibe Online -- Auslandsforum ‘classic’”, → here is the discussion.

It continued like this:

I was at the FEVE ticket office in Ovied\o, a little short of time to the train to León. Filled out a form handwritten with day, train, time, contact information, and text what was going on. There were two copies for me, the original was kept. The person at the counter copied my tickets and kept the ticket’s copies.

So let's see what comes, maybe I write to the RENFE/ FEVE an email also.


By the way, it went on in the train León-Bilbao: Conductor and her collegue had no idea. They then did a phone call somewhere. Thereupon they studied the InterRail ticket profoundly and whether everything was filled in correctly. Then she asked me via online translation if I had paid in other trains of this kind -- which I denied (to tell I had paid, but incorrectly, would have been too complex with the language barrier, besides, I have already claimed it under approval of an employee in Oviedo, so I think the “no” here is OK for practical reasons), and I also showed to her → interrail.eu/es/plan-your-trip/trains-europe/railway-companies. Thereupon they typed again in different devices and phoned, and then it was accepted.
 

After a change of conductor, the new one did immediately recognise and accept the ticket, as well as did the person in the ticket office in Bilbao which I had to ask to let me through the barrier.

.. upcoming information I will provide in the German forum in → this thread, only, so if interested follow there.