Japanese sencha seems to lose flavor after 1 day of opening!

[LeoFox]

It is shocking to me how sensitive japanese green tea is.

I open a bag and the tea is great. I store it in original wrapper clamped with most of the air smoothed out, and then place that in an airtight sealed canister. Next day, tea has lost maybe 30% of its flavor. These are senchas from o-cha harvested this year. What am i doing wrong?

[Lyuluck]

If unopened, store in the refrigerator (or freezer) as is. However, be careful to return the tea from the refrigerator to room temperature before using it. ...
After opening, transfer to a container with light tightness and slight tightness, and store in a cool and dark place.
As a general rule, tea that has been opened should be stored in a cool, dark place that is not exposed to direct sunlight. Tea is vulnerable to oxygen, moisture, heat, and UV light and will deteriorate quickly if stored incorrectly. This time I will tell you about the correct method of storing tea.

[LeoFox]

If unopened, store in the refrigerator (or freezer) as is. However, be careful to return the tea from the refrigerator to room temperature before using it. ...
After opening, transfer to a container with light tightness and slight tightness, and store in a cool and dark place.
As a general rule, tea that has been opened should be stored in a cool, dark place that is not exposed to direct sunlight. Tea is vulnerable to oxygen, moisture, heat, and UV light and will deteriorate quickly if stored incorrectly. This time I will tell you about the correct method of storing tea.

Thanks for the suggestions. Actually, I have been doing exactly as you say and still experiencing this problem.