What the heck is going on here?

Yeah, that's a little rare, but 45 degrees was pretty common. I used to work on a 97' MY that drew 8.5-9' and we used to travel mostly on the intracoastal waterway and in GA and stuff it would happen probably once a day. Also it always sucks you towards the shallow side. The boat would also list at it did this a little bit. You realize it, bring the throttles back to idle or close and counter steer and it turns back.

I've also had it happen on the 75' Hatteras MY at the turn on the bank in front of Cat Cay at low tide, there it just swung back and forth about 60 degrees total without touching the helm.....till I slowed her down to 7.5 knots for a couple of miles till it started getting deeper as you go East and she tracked straight

We help on a 92' Mathis-Trumpy on the Ortega river and Jacksonville. MY Innisfail. must be operated dead slow in shallow water. Any +/- slope or mound in the bottom, she will drift sharp to follow or push away, if your not on top of her.
Less than 10 feet, hang on.
15 feet she is a queen.
20+ feet an Angle.

Some things haven't changed in 77 years.

ANY deep vee boat and fairly deep draft in shallow water at hull speed will do the same. Some more than others but they will all suck bottom and turn. If you're on plane the same boats won't do it. But take a Westport at 10-12 knots and go through an area with 3' under the keel and it will do the same.

I know Innisfail, she used to sit on the New River. She's probably the most beautiful Trumpy built.

Up here in my hood.
She makes most of the failwire home games.
Sure looks good out on the StJohns river.

They tend to wander if they have a keel.....ones without a keel tend to just turn towards the shallow area from what I've seen.