Just some observations:
I have a 2015 24Kwh Leaf so am long out of warranty, but have observed similar loss of power/turtle twice while having a fairly high load on the pack.
Once happened at -15F and the other around 3 degF. The first time I was just taking my Leaf out for the 1st time in cold like that to so how it handled it.
The more recent time it came as sort of a surprise, but I hadn't charged or used the car in over 36 hrs so sat with almost a full charge through temps much colder. I think the battery pack cooled to around -14 or so and the weather only started to warm.
Unfortunately I did not have Leafspy active on either trip.
I think what is happening is the load on the cells exceeds what they can provide at the temperature they happen to be at. Because the pack has a fair bit of thermal mass, it takes a long time for them to cool or heat.
In my case that meant that even with the air temp starting to moderate, then core temp of some cells were still cold enough to cause a problem.
Normally they are charged during the night, and I think this prevents the core of the pack from cooling enough for the problem to show most days.
I think the critical factors are the load, 10% grade is far above what I was driving on, and the core battery temp. These two factors come together to cause the problem to show at higher temps for some then others.
I may be wrong, but I don't think this kind of "problem" sets a DTC, rather when the load is removed the "problem" is considered resolved and no record of the problem remains in the DTC memory.
This leads to a big problem when the car is taken to the dealer, and no or unrelated DTC are in memory. At far too many dealerships, the rule is "no code= no problem" and no further time is spent trying to resolve a "non existent" problem!
It is very hard to see how a telemetrics comm problem could cause a loss of power!
The problem is the dealership personnel not putting the effort into reproducing the problem.
In this case it would involve operating the car under the same conditions that cause the problem, namely a "cold soak" of the battery, then driven briskly up the 10% grade.
Needless to say there are many monetary incentives to "sweep the problem under the rug" and deny there is a problem.
It has been close to 5 decades since I worked at a dealership, but I doubt how mechanics are paid has changed much. Diagnostic time is not paid for, it is supposed to be included in the rate for making a repair, but never covers putting in the time to diagnose complex or difficult problems, so you end up with "we couldn't reproduce the problem (with the car sitting still in the mechanic's bay) and there are no trouble codes, therefore there is no problem!
50 years or so you could petition the Mfg "district rep" to mediate the problem. They are salaried employees of the Mfg and if good, can spend the time with you to reproduce the problem.
This, however can be problematic as well as you need the weather to co-operate on the day and time the district rep is available.
In my case both events happened with the heater running on full and going up a modest hill around 55 mph, in short order maximum load on the battery, that I would put on it for my usage