Do dragon Habits reset every Reign?

No, Habits are permanent. Like Star Rank, they never reset between Reigns (the 8-week seasons). Everything you invest in Breedmarks and rarity Cores to level them is won for good.

That's what makes Habits one of the best long-term investments in the game:

• they stay leveled Reign after Reign,
• their materials (Breedmarks, 🔵🟣🟡 Cores) are permanent in your inventory too,
• they weigh enormously on a dragon's real strength.

By contrast, your dragon level and your research reset every season. So late in a Reign, putting your resources into Habits and stars is always more durable than into levels or buildings.