Opens are really tricky. They only register when an actual download of a Pixel happens. For example, if someone is previewing the email, it wont trigger. It is possible that you are doing a test sampel versus, selecting al ead and doing a flow action against it, but functionality aside, I would recommend a stronger trigger than an open.
To fix your trigger:
1. Try an actual flow action against the lead, then open it by double clicking and downloading images which might be in the email 2. Make sure its not just a text email etc.
You have made a flow such that you request a campaign whenever you open the email. The following is the screenshot of what we see when we request a campaign;
This process has two parts in Marketo - "Request a campaign" and "Campaign is requested" You need to define the the source/Flow under "Campaign is requested" to complete the process. The following screenshot highlights"Campaign is requested"
Make sure that you have defined the source (Flow action) Note that "Request a campaign" is under Flow and "Campaign is requested" is under Smart list.