I've been thinking about that ultra short flight time problem and for me it keeps coming back to the age of the batteries. Lipo's are limited in two ways, number of cycles and age. On an average they are good for a couple hundred cycles or a couple years on an either/or basis. Since the 920 was originally released in 2015 it's possible the "factory" battery supply for the 920 was only a single production run, with all the batteries now being sold coming from the original two year old inventory. If that's the case then all the new batteries are pretty much done the day you received them.
There's a company named Max Amps in Spokane, WA that makes extremely high quality lipo battery packs. A quote from their site is pasted below:
"We are the number one manufacturer of custom LiPo batteries for RC hobby and commercial grade quadcopters and rc vehicles. MaxAmps Lipo batteries are the best way to upgrade your DJI and Traxxas batteries. We can custom build with any voltage or capacity you require and we use only the freshest LiPo cells."
From personal experience I know they have been used to power military grade UAV's to test the possibility of converting from gas engine power to electric power and proved themselves as a very capable battery. They are not the least bit cheap, but very reliable and they will make custom packs. I have used them in the past to make and ship some large lipo's on short notice in order to meet a time critical demonstration. They always come through. They are a possible alternative to aged Yuneec inventory. Pricey, but possibly worth it.