This should be ok. But yeah lets see the photos.
If there is any way you can run an idler on that motor mount it will help the belt mesh better with the pulley and reduce excess load on the belt. I have seen some people put an idler on one of the motor bolts.
I get my belts here, but there standard is 15mm wide. Your setup looks like it might fit a 15? Or ask them to cut some 12mms for you.
Honestly from my perspective it looks like you’re using 5M belt on 3M pullies… Where did you get them from
that would definitely cause some issues…
yesterday was helping someone figure out what type of belt they had just purchase from a kit, i assumed it was 5m but after reviewing the link, sure enough was a 3m setup. Good look/observation @ShutterShock, so to all those buying kits online (elsewhere) be sure to DBL check that info. [the particular item i was reviewing was stated to be for a scooter, but very similar to esk8 setup]
Awesome yeah so just get a 3m belt and you’re good 
the pulley is torqueboards 14t 12mm pulley that comes with the v4 mount/drive kit collections/single-motor-mechanical-kit/products/single-bolt-on-motor-mount-w-drive-wheel-kit says there HTD5
if its not from the alignment issue im gunna be stumped
revisiting this topic, Recently my build happens to have not aligned belt, fairly long 275mm. about 1-2mm off and scrapes side of pulley making some pattern on, making squiky noise I really risk myself and put it to the test. I went about 60km in range went 30mph+ So far i don’t have any issue, sure it got hot a bit but nothing major. and the belt went through 2 month of use prior to the test. I found, to shred like your picture, belt have to be loose a lot. if it was too tight, it will snap off. And I also do think the pulley looks 3 not 5 but could be the picture problem