one thing to mention you seem to not be measuring the wort its self but the air or water around it, the banana flavor is a direct result of high wort temperature meaning the water or air was correct but the wort raised its temps too high while fermenting, this is hard to measure as a new brewer but the wort is what we measure not the anything else. for best results you use a thermocouple inside the fermentation vessel and measure the wort its self, good luck hope it gets better in time