Heya, just to close the topic on my end. It turned out that inverter input mosfets were shorted and respective controller was fried (due to drain to gate short on the mosfet).
I replaced both mosfets (Q6 and Q7) with CSD19506KCS.
The new ones are much oversized, but thanks to much lower Rds(on) than the originals heat up less also.
Controller was replaced with the same UCC27424QDRQ1.
I have similar issue, though i am a technician but discovered that the charging mosfet side is short circuited. Upon replacing the Mosfet dp8974, it worked on battery for hours after coupling back but when i inserted the AC charger, it was charging fine. As soon as i removed the charger and turnnon the device for use. The device went off and shows short
What could be 5he reason for the fault as my location is remote and cant easily have access ro your customer service representative. Kindly help as i am already enjoying your device and recommended it to friends and families