Performance and crashes while editing and exporting on mobile device

New problem here. I've been trying to work on and export this video for the past 2 days. As usual, it has been lagging and crashing the whole time. Crashing while creating the video, and crashing while exporting. Anytime I added a clip, or audio, transition or applied a color correction, the app crashed. I finally finished my edits. Exporting was a hassle cause it would crash, either before I exported, during or after. If it does export, my video looks grainy and distorted. See attached photos. There is this black grain over my video. 

This has not been fun. I have made sure my phone is updated, the app is updated. I have restarted countless times. I have removed all my previous projects, I have tried deleting and restarting the app. I have around 900 GB of free space on my phone. What else can I do? 

Mod note: Title changed slightly.