Which are the heroes that you each have selected as low-priority?
It's possible your friend has high-pick rate heroes like Haze or Seven as their low-priority slots, which will almost guarantee they get Lash.
Based on some comments I've seen in the subreddit, some people intentionally do this...
Definitely an issue right now and happened to us last night, sucks. The root cause seems to be that Party Matchmaking tries to match parties with parties when the skill gap warning is active, and since a solo queuer is not a party, it can't make a match.
I initially thought this sounded like a fair practice too but I feel like it actually only matters at higher average MMR games, where being left out of voice is definitely suboptimal for your game.
Regardless, I am wondering if it would just be fair and an acceptable solution to match a 5-stack...