Welcome to ECF. Your tastebuds may be "deadened" to the flavor after you vape a while. You are also using fairly high wattage and low resistance builds so I'm going to assume you are very much flooding your system with vapor. If you are chain vaping, it's also possible you are over heating your juice a bit, and that may be the cause of diminished flavor (some flavors don't hold up well in high wattage applications).
I might consider the latter point, if it's a case of fifteen minutes of flavor, and then nothing you do causes the flavor to "return." I'd also maybe try a rayon wick as it holds up for longer (timewise) but also handles higher wattage vaping better without cooking the wick. That (may) help some.
I would, like some of the posters above, maybe do some experimenting with different tanks and try one that is a little more restricted as far as higher ohms and lower wattage, to see if doing that improves your vaping experience, plus you will have a backup if needed and you can rotate your setups and flavors if chain vaping so your tanks will not overheat, and etc.
Best of luck and welcome to ECF.
Anna