I've been struggling a bit so I post it here if you happen to have the same problem.
I had no data on my LG G6 since Android Oreo 8.0 update, and tried a lot of things (reset to factory settings, removing SIM, etc...)
What worked for me was manually entering APN, as stated on this Fido website :
Many thanks for posting this solution. I just purchased unlocked LG G6 phone with the Oreo update. No data connection from Fido. Only WiFi. Tried your solution and Bingo, All is well again.