Liquid start tasting very bland after 10 days

Hello,

ive been vaping the same juice with same % aroma concentration (25-30%) in few devices for 2 months.

My last device, Thelema Dm45 with 0.6 single mesh coils, seems having hard times. I took a new coil 10 days ago, put the liquid in it and it was tasting great. After 10 days of moderate usage (150 puffs /day max) now the flavour is really bland (i can taste the custard cookie and milk but it's very bland, like when you put a lot of water into a glass of wine).
With another device (ursa nano 2 0.6ohm cartridge) there was no issue like that, even tho a pod lasted like 14 days.

It is a matter of vg/pg ratio? Or a matter of different coils construction?