Rumors that the train track between Nanu Oya and Ella is under repair?

You are right to check, January often sees track maintenance after the heavy Northeast Monsoon rains in December.

Current Status: As of this week, there are intermittent disruptions between Nanu Oya and Bandarawela.

The "Bus Bridge": Sri Lanka Railways is currently operating a "bus bridge" for some scheduled trains. This means the train stops at Nanu Oya, you get off, board a Railway Bus for 45 mins to bypass the damaged track, and re-board a train at Bandarawela.

Recommendation: If you have heavy luggage and kids, skip the train for this specific leg. Hire a private driver from Nuwara Eliya (Nanu Oya) directly to Ella. It will take 2 hours by car vs. 4+ hours of stressful transfers. The view from the car is almost as good!