Alternator Issues On Kia Sedona

Hello!

I have been having issues with my 2017 Kia Sedona lately related to what I believe is the alternator. It started having power issues a while back ago that it would struggle with accelerating and driving. Then one day, it just completely died out after a day driving around. I got it jumped off but it died again. Tested it with a multimeter when I got it towed home and the battery wasn't getting charged (12.4 V idle).

I replaced the alternator with a new Carquest alternator, and it tested well after with a solid 14.3 volts on the battery when idle. But, when I test drove it, it started having similar issues and when I tested again, it wasn't charging again. If I take off battery and let it reset after sitting awhile, the alternator will work again. I checked connections, found the positive terminal was pretty loose (apparently this is a common problem with this car and aftermarket batteries). I shimmed up the terminal and even got a new battery. It drove better with the new one but when I got home I tested it again and the car was at 12.5 V. Took off the battery, let it sit for a while, then alternator works again.

Is this a bad alternator from the box or could this be an issue with the ECU? All fuses tested good with the multimeter so far.