Oh I forgot to mention that I may have healed between my first and second attempt. It's been a bit since I did this, so I'm a little fuzzy on the exact details.
Interesting! I will look into it further and see if I can make sense of it.
Sure! I had a Yamask as part of my in-game team, so it was fully healed and around level 50 before I used the damage method. I had wild Pokémon attack it until it lost a little more than 49 HP, went under the ruins, and it didn't evolve even though I was sure to double check requirements. Its health bar was yellow at this time so I got it to red by further battling. I went under the ruins again and it worked.
I also searched twitter with the terms "49" and "yamask" and there seems to be other people who have issues with this. Though I can't personally attest to their methods.
Can you be more specific about what you did? A friend of mine, for example, took her Yamask out of the PC with the damage that she inflicted to catch it, but that wasn't sufficient - it had to be new damage.
Galarian Yamask's evolution method doesn't work at high levels. I wasn't able to evolve mine until the health bar was red.
