If pingback then no TimeToInteractive?

[doronin]

Hi
if I do request to private instance without pingback
npx webpagetest -s http://private.com/ test -y Native -l somelocation -N 20 --timeline --video --first --htmlbody --chrometrace --ignoressl https://www.upwork.com/
I get TimeToInteractive in result.
But if I do the same request with pingback:
npx webpagetest -s http://private.com/ test -y Native -l somelocation -N 20 --timeline --video --first --htmlbody --chrometrace --ignoressl --pingback http://pingback.com https://www.upwork.com/
I couldn't find the TimeToInteractive in the result data set.

Any ideas?
Thank you.