CloudFront to ALB connection

Hi,
I set up CloudFront to serve static front-end from S3 and need some dynamic back-end as well. So, I set up redirection for some requests to ALB as origin (ALB runs Lambda) with cache disabled. Direst requests to ALB work fine and fast (~200ms), but when requests go to CF, only ~50% really work. For other 50% CF returns 502 and ALB doesn't receive any requests.
My location is close to ALB region, so delays shouldn't be.
Tried adjusting TLS versions, forwarding to ALB "native" dns as well as to custom subdomain. The result is the same: half of the times connection doesn't happen. When it happens - it works fast.