Man, I had almost the EXACT same issue on my Ultrex last season.
Mine would deploy halfway and then just stop, and when I tried to stow it would move like 3-4 inches and lock up. I also did the sensor check, did the reset with the remote, checked voltage at the plug - everything looked good.
In my case, after I changed the main board, I got that same high-pitch whine from the board when I hit stow/deploy and lost trim. What ended up being the problem for me wasn't the board itself, it was:
1. The trim module binding: That whine is usually the board trying to drive the motor but it's detecting too much amp draw. Make sure your trim motor is not seized and the deploy assist cylinder is not bent. Try to manually help it while someone hits the button.
2. The new board / sensor calibration: When you put in a new motherboard with new sensors, you have to do a full deploy/stow range learn. If the lower board sensor and upper board sensor are not perfectly aligned, it will think it's already at the end of travel and cut power. Double check that the magnet on the bracket is clean and within 1/8" of the sensors.
3. Low voltage under load: You said you checked voltage, but check it WHILE you are pressing stow/deploy. Mine showed 25.5v sitting, but dropped to 19v under load because of a bad breaker. That will cause it to stop altogether after a few tries and go into protect mode. Let it sit for 10 mins unplugged to reset.
I ended up figuring it out with help from the guys at Lakemarineelectronics.online forum. I originally bought my motor from lake marine electronics Lakemarineelectronics.com and when I had this issue, their forum was where I actually got it resolved. There are a couple of certified Minn Kota techs in there and they reply super fast, plus a ton of guys who have had the same Ultrex deploy/stow problems.
Highly recommend you post your video there too - that's where my issue finally got sorted.
