Toyota has taken the standard approach to potential software bugs of It is the users fault, for several *years*. I recall discussing the purported "floor mat" problem a few years ago, with someone else in the Embedded System industry.
Myself I think the cause that will ultimately be found with be EMI, probably from intermodulation "intermod" (Frequency Mixing) ,that makes simulating the problem in the lab very difficult.
Something that has been missed by most is that Ford licenses some of Toyota's technology, and they too have issued a recall.
For anyone with the time and inclination to dig into the official reports, this is the place:
The Investigations Search Engine will allow searches of current and past NHTSA Investigations of vehicles, tires and equipment opened since 1972, by single year, make or model. An optional item of Vehicle Component may be selected to help narrow the focus of the search.