I updated to 2017.08-1 and tried playing back a file from a USB flash drive and it plays back fine. Disconnected the HDD from the router and connected it directly to the Vero, and files play back fine. Something must have changed with my router that the Vero doesn’t like, but none of my other networked devices have a problem with. I’m not sure where to go from here exactly, but the Vero is not at fault.
Also, HD video plays back fine, so I’m gonna stay at the current version.
There is no option for me to set the samba protocol in SMB client settings, even in 2017.08-1. I did manage to connect to the HDD just fine manually, though.
EDIT: Very interesting development. I thought about what the difference was between the Vero and the other devices on my network that I tried playing video files from, and the only thing was everything else was Wi-Fi and Vero was Ethernet. I connected the Vero via Wi-Fi and now videos play back fine from the network HDD. I feel pretty dumb I never even thought to try this earlier.