No, this is not at all normal. There must be something strange going on here. Were the morning readings consistently sharp or consistently flat? Or were they all over the place? Is the tuner actually giving readings in cents? Is it possible that the tuner settings were changed? (Say, from A=440 to A=445.) Did the melodica actually sound that far off tune to the ear? Do you ping each reed after scraping it? (Not that this would make such a big difference.)
It is not unusual to get different readings a day later or even an hour later, with an occasional reed off by several cents, but not by 30 cents unless the particular reed is failing. The reeds would not all be failing at once.
If you check your melodica tuning every day, you’ll go crazy. But 30 cents off is way too much.