Recurring: Red Triangle + Engine Light: Car won't go into gear

Dec 2017: While driving 70mph on the highway, I ran over a bump and various lights came on the dashboard. I was scared so I pulled over on the highway. After turning the car off and on, I was unable to switch gears. Pretty sure engine light and red triangle was on. Took it to a garage, they hired an electrician to check it out. They charged the battery and told me the cable was not secure.

August 2018: Car would not change gear. Red triangle and Engine light and a couple other lights came on. Took a taxi to school and came back in 2 hours, then everything seemed fine. I drove it to dealership and they told me 18 codes were diagnosed. They charged the battery and drove it for over 3 hrs. and there was no problem. They said it was probably the catalytic converter, so I replaced it.

October 2018: Car would not change gear. Red triangle and Engine light and a couple other lights came on. This time, I was able to get the car going after 20 minutes. Unfortunately, as I was driving 50mph for 1 minute on the highway, car seemed to have gone into neutral. I could not accelerate at all so I pulled over Same problem, I cannot change gear. Brought it to dealership again and they are still unsure what to do. They said the problem has to occur while their machine is plugged into it. They will charge the battery and try driving it around. I told them my battery is probably leaking.

Is this dealership incompetent or is it really that hard to diagnose the problem?
What do you think the problem is?
What should I do?

Thank you in advance,
Kyle