Bought Shizuoka matcha from Donki – some sachets oxidised?

Hi all,
I picked up the Jonetz own-brand Shizuoka matcha from Donki on my recent Japan trip. But I’ve noticed something odd: some sachets seem oxidised right when opened – dull yellow-green colour and bitter taste. Others from the same range are totally fine – vibrant and fresh.

What’s confusing is I bought the exact same matcha from Donki in Malaysia last year, and every sachet was perfect.

I store all my matcha in a proper airtight matcha jar from Japan, so it’s not a storage issue. Could this be a packaging fault or something to do with transport?

Bit of a shame, but I’ll still use the duller ones for drinking (I don’t really bake).

Just curious if others have experienced this with Donki matcha. Might have been bad batches but still a shame!