My highest before was Moira at 25 and sat like that for nearly a year so was very surprised to hit 29 in one round of push the payload with 6k damage and similar heals, obviously next round I died about 8 times with only a couple elims but oh well who cares I just hit a 29!!!
I know, nobody cares yada yada but wanted to share anyway, thanks for reading.
My best killstreak was 72. It was 69 before that, but I just had to go and ruin it like a loser.
…long enough to be the villain…
A 72 is crazy, I pretty much only play Rank as support and not sure those kind of numbers in one round are possible unless Moira and getting tickle elims.
It was not impressive at all because the enemies were obviously not particularly great and that is counting both rounds.
I do not remember any single round result except for my first 35 killstreak because I kept going without dying and when I checked the stats it just said 35. 
That’s why I started just using whatever the scoreboard said because the first one was a flawless 69 and 0. I died right at the end of the 72 streak. 
My streak was actually against a very good team, the battles were long so more time to kill and my little star things were just landing more than ever, we almost lost in in the 4th round.
As for a streak continuing into round 2, I’m sure they reset for me but maybe it’s a new thing because I’ve finished games on Moira 40+ for 0 and elim streak always stayed the same, definitely got 30 on kiko that game too before dying.
Edit/ I think you’re saying same thing maybe, like your record says 35 but you go with scoreboard because technically it is a streak even if not recorded?
I’m not sure what my scoreboard streak is I do it the other way, could be up to between 50 or 60 was a Moira main for nearly 200 hours when started this game and destroyed the early ranks till wanted play high skill high reward characters, no ez mode.