In addition to David's recommendations, I'd also check the following:
1. Priority score of the campaigns- make sure that visitors that match the target segment are not seeing other campaigns with higher priority.
3. Does the target segment include specific URL or matches visitors on all pages? I'd recommend specifying the URL also in the segment level. You can also randomly check a few match visitors and see what pages they viewed and verify they actually visited the target page.
A few ideas but more details needed here:
You correct in saying it should be more or less equal impressions 50/50 for 2 campaigns that are ab tested.
Were the campaigns started at the same time? Are they both set to Launch and not Scheduled or Scheduled at the same time?
Are they targeting the same segment (which they should be)?
What type of campaigns (Dialog, Inzone) and check the target URL making sure the campaigns are showing up upon segment match and the visitor is seeing them (impression).
Those are just some ideas and checks, best would be to send through a support ticket, with the campaign details for further investigation.
Thanks for the response David. Reponse to your questions.
1) Yes, both were launched on the same time. Schedule was not set but just launched at the same time. I am checking the week on week report too, every week there is difference in the impressions
2)yes, same segment is being targeted, which is all users landing on the targeted page
3)These are inzone campaigns and target URL is same in both the campaigns (which should ideally be ).. I checked randomly and found that campaigns shows up on the visitor match