I’ve hacked a portal everyday since the epoch badge came about. I looked and it says my current hack streak is four days. That is not correct
Does your Epoch badge say 40? Then everything is as it should be, after 7 days, you complete a hackstreak, your Epoch gets a +1 and the hackstreak resets to 1 on the next day. If you hacked every day since Epoch started, you should have 40 on the Epoch badge and have a Hackstreak of 4 under the "Now" tab.
I'm having the same issue, just noticed my hack streak reset completely, yet I do remember hacking a portal the day before, i should be on 5 day streak today with 321 days.
Epoch and sojourner works differently.