Glad the tune-up resolved your chain drop issue. How often had you been cleaning and lubricating your chain?
For mech bikes and hub motor drive ebikes, replacing the bottom bracket is fairly straight forward and a routine part of long term maintenance. With that said your bike has the Yamaha mid-drive motor, does it not? The function of the bottom bracket (connecting the cranks to the frame) is integrated into the motor bearings. A Giant dealer would be best suited to take a look at this to see if your motor needs any adjustments, but with your mileage I wouldn't expect anything major.
BTW - Other mid-drive ebike owners, like myself, are reporting that the extra strain on the chain is requiring chain replacements as often as every 1,000 miles depending on riding conditions. Something to think about...
I ride around 80km per week, and I usually clean it every 2 weeks. everything is original on my bike, as i only got it last September. I dunno the exactly km because it doesn’t have the lcd display. My battery has 26 cycles, so i think the lifetime mileage is around 2000KM (each cycle gets me 70KM, so 26 X 70 = 1820)