Session variables destroyed while making contribution through webform in Drupal 8
I think session issues sounds more like a D8/CiviCRM configuration issue rather than a D8WFC module issue.

I just confirmed that D8WFC can do live payments (authenticated and anonymous) with iATS Payments. I'm sorry we don't use any Omnipay processors with any of our clients so I can't try to confirm your scenario. Perhaps check on Mattermost -> chat.civicrm.org Drupal channel to see if you can find others who can reproduce this. Some folks in that channel are system administrators themselves and may be able to help. 

Here's an example of a live-payment -> with a Confirmation that all lands in the database using D8 CiviCRM Entity: