Oh a bunch small things.. hmm.
The lower box needed additional bracing right away to stop rotating, the controller power switch died twice. Had a BMS that died mid-ride... been without one for at least half or more of those kms. Lithium Phosphate batteries though (safer), and I only run the battery between 30-90% charge.
What else... few broken spokes on the back wheel, should've used normal bicycle spokes probably. The straight gauge 11ga spokes (straight gauge in general) don't tend to flex at all and can snap near the ends. Been missing a spoke for over a year now, whatever 36 spoke wheel it's fine.
Bunged up the rear hub bearings by accidentally bottoming out the back wheel on curbs (accidentally ripped the throttle going up one once and smashed hard), rim was fine, it's burly.
Wore out a lot of rear tires near the bead due to the cornering torque. Most 24x3 tires have paper thin sidewalls though. I've had only one flat during a ride that I had to walk home from (only a couple km), but had a half dozen flats total that I was either at my work shop or home when I noticed it was flat. Usually the valve tearing from the tire/tube rotating on the rim under torque.
Hmm, some of my daisy chain connectors have broken between between the separate battery banks, I think twice from being under too much tension/vibration.
Burned out my rear tail light recently by forgetting to turn the bike off while it was charging, as it couldn't handle the peak voltage.
Rear bmx style free-wheel has died and been replaced twice now, that's just kinda normal wear. Only on the second chain.
Those are most of the issues I think, and a bunch of other things were just modifying and changing components out to improve the function and comfort of the bike.
It's been surprisingly reliable so far! But I spent a decent chunk of $$ on quality MTB and electrical components, as well as did tons of research before building.