How is it the dealer's fault if there's no codes and no indication of a problem? You want them to tear into the transmission on the off chance they might find something? With today's cars, that sort of repair attempts are impractical. Depending on the part (such as the CVT), dealers may not have the specialized tools and training to dive deep into it.
I'm not saying some dealerships aren't lazy, but to begin troubleshooting you have to have somewhere to start. I wouldn't want to have to pay for that sort of work if nothing can be found.
The dealerships are supposed to have updated information and diagnostic strategies in place and train the technicians to use them. The problem is lazy thinking and trying to make $$$$, both for the tech and service manager. The techs don't want to spend a couple or more hours on diagnostic testing when they only get paid an hour to do it, so they guess or assume and often change out complete systems in the hope that the problem will be rectified.
We've got a Nissan Murano AWD at the shop now. No codes on any system and bucking while driving like it's misfiring. Two people spent a lot of time going over this car to narrow down the issue. Both believed it was the transmission, a CVT, but couldn't say for sure. They've been doing diagnostic and repairs for a while and went through the module test, wiring, grounds, battery, engine management, transmission controls, etc.. The car would not act up on the lift and data logging didn't make anything apparent and certain. So, after I got a moment between cars I drove it. Acting like torque binding. In turns it was worse. Bucking in straight line with torque, cruising, and rolling in Neutral. Transfer differential is shot and needs a rebuild. The owner doesn't believe that it's the transmission because it acts like a misfire.
If this car was at the dealership, they would have charged the owner for unnecessary engine work because of the way it acts without looking for the real cause which would remain after all the work and cost to the owner. If the car was under warranty, that just means the owner doesn't foot the bill, but the techs still get paid, even when they misdiagnosed, or guessed wrong. And this is a problem because it leads to continued practice of guesswork instead of finding the real issue the first time. You wonder why your car is at the dealer so long, well, it's because they have your car in the bay and their first attempt at rectification failed so they've moved on to trying something else. "We're working on it" really means they can't find the issue and what they've tried thus far didn't work.
I'll give you another: A Jeep with a Hemi has codes for MDS solenoids and cam actuator. The dealer said it needed an engine. The engine NEEDED a pigtail harness that runs the MDS and cam solenoid because the one on the engine was frayed and shorting out at the connector behind the cylinder head. A $70 part and an hour to fix. That's not much compared to the cost of an engine and the labor to change it.
Lazy man works the hardest. And there's a lot of lazy men, and women, at the dealerships that try to take an easy way out and are more concerned with their paycheck than their work. Sometimes diagnostics is easy, sometimes not. It all depends on the person doing it and what their true aim is. For me, I love the puzzles. Give me a car without codes and I go old school and find the problem. But there's not a lot of people like me out there. So you take your chances.
On the OPs issue @GBMaryland
It seems to me that there is an unclear explanation as to how things transpired. I understand that in times of stress things seem to be in fast forward with a lot of things happening at once. So I want to ask, did the engine stall or did you shut it off and restart it? Was the engine running as you tried to get forward motion? If so, was the rpms going up without applying torque to the wheels to move it, or was it getting partial torque like it was slipping gear application? This erratic shifting you talk about, can you expand on it?
If the engine continued to run, that eliminates engine issues, but not communication.
If the engine sped up without transfer of torqued, that is either a communication issue between the ECM and TCM or a mechanical issue within the transmission. There are several things that can go on mechanically without setting a code. Torque converter failure doesn't always set a code. How many owners had a CVT or otherwise that had the shuddering torque converters and never had codes? Then there's slipping pulleys that if the pressure value reported to the TCM is within specs will not set codes. You also have broken parts where everything in the CVT is good but the outputs aren't able to function, such as broken CV shafts, broken gear teeth on the diffs, etc. Not everything has a monitor connected to it. If your dealer cannot find the problem, it's not the car's fault. It's the technician in which case you need another set of eyes on it. Contact SOA and get someone else to look at it or find the right independent tech that knows how to track these things down.
And I'll give you a bit of advice: All manufacturers are going to CVT because they help reduce emissions by keeping the engine running at a smooth torque transition instead of the constant shift in engine performance with a conventional automatic or manual transmission. They are constantly trying to update the operation of the CVTs through mechanical engineering and the software that runs it. So just like the times when autos first appeared, there will be issues after production that don't come up in R&D; just like any software, in any system whether car, office, home or your phone, glitches show up. Shite happens with cars and you have to roll with it. Is it frustrating, yes. It disrupts your commute, your schedule, your weekend sometimes. This can occur with any manufacturer's vehicle. It's not a problem just with Subaru. Trust me, I've seen a lot across the board in American, Japanese and European cars. It's all of them.