It tasted better yesterday
The same tea, brewed the same way as far as you remember, is noticeably worse than it was last time.
Likely cause
Something in the method moved and was never written down. Leaf weight and water temperature are the usual suspects, followed by the water itself and how long the cup sat before you drank it. Your palate also varies with what you ate and how tired you are.
Try this now
Brew it again with everything measured, and check your last note for what you actually recorded. If the note has no conditions in it, that is the finding.
What to change
Record leaf weight, temperature, vessel and time every session. A tea that seems inconsistent is usually a method that was never fixed.