Disney hasn't offered much. Posters are speculating and in some cases making up facts out of thin air. We don't know if Disney was lying or if the CM making statements was telling us what was known by that CM at the time the statement was made. We have no idea how much hotter the gondolas got after sitting or 3 + hours. I haven't read any first hand reports suggesting oven like conditions.
What do we know
The Skyliner Disney is using has been used successfully in locations through out the world.
Doppelmayr employees were on site for the construction and training. What's different about Disney vs other installations. A significant number of Disney guests use
ECVs. Many, probably most, of those guests rent their scooters in Orlando. Some (many?) only use the scooters when vacationing in Disney.
ECV users have different skill levels and experience levels. Disney thought guests, either in the special loading areas in most stations and the slower moving gondolas in the Riveria station, could board with ECVs and strollers without having to stop the line. We know CMs were telling parents with double strtollers to fold it before boarding. We know from posters CMs were generally stopping the skyline when ECV guests were boarding.
Some reasoned assumptions. Guests with ECV are expected to drive onto the bus. The driver is only required to secure the ECV. Almost every time I've observed an ECV boarding a bus the driver either moves the ECV enteriely after the ECV is driven on the bus or substantially assistes the guest. It's plausible the typical ECV guest isn't capable of driving the ECV into the gondola and/or backing it out at the other end in the time available at the Riviera station without having to stop the line.
Solutions might include positioning room assignments so CBR guests generally board at the CBR station. Disney may need to have CMs load the ECVs How many ECVs can be loaded at once in the Riviera station? Stop the line and load that many ECV guests at once. Repeat after you have that number of ECV guests waiting.
Is it possible the frequent E-Stops isn't generally experienced in other locations. Could those stops have caused some mechanical issues.
edited to add: Also possible constant starting and stopping due to ECV loading caused CM to routinely hit restart buttons without following procedure. Certainly possible ECV loading had nothing to do with last nights issue and is a separate issue.