I just switched from a S8 to a Note 8 and I'm surprised that the 'Just Once/Always' option is gone... I'm confused as to why they would keep it for the S8 but not the Note. Am I missing something?
Try going to Setting -> apps and the : dota and then check default as well as clear defaults from the app(s) you want it to ask. It may be set to automatic.
Theres a chance your restore from 7.0 backup to 7.1. played a role. Smart Switch is the smoothest method.