I'd start by disconnecting and inspecting each cable. Get a can of QD contact cleaner and clean them all really well. Throw a dab of dielectric grease in each one as you reconnect them. Make sure they're seated tightly. Pull the battery out of the cradle and inspect those contacts.
If you...
I've been running Bolton's 35a controller and color lcd kit (LCD8H) for about 40 miles now on an other-wise stock 2018 Rad Rover (14-34 free-wheel). The acceleration is awesome. I can now draw 1200w+ for a short time when I start accelerating. My top end isn't affected much except when I'm going...