FYI this is answer I have received from Support. We have decided to go ahead with a variation of suggestion 2.
We noticed the "Click Email" activity actually gets in later than "Form fill out" as we noticed that the activity ID of "Click Email" is 315618166 which is bigger than 315610814. Even though the timestamp of these two events is on the same second. When we evaluate form fill out, the click email is not recorded yet, so it will filter out this lead from campaign. This is a common mismatch between customer expectations and our behavior. Apologies.
If the link in the email redirects to the form in the campaign, this will happen quite often. Our email activities come in with a delay, but form fill out activities comes in real time. To resolve your issue for future similar campaigns, we came up with 2 different workarounds that may work better for your needs. Both workarounds will require the removal of the "Clicked Link in Email" filter. Please try them and let us know what your results are.
1. Put the filter of "Click Email" as a step choice in flow. This way, by the time the campaign is triggered and picked up, the email click activity should have come in. However, the drawback is that you won't be able to specify the exact link. To be even safer, try putting a 5 minute "Wait" flow action as the first step in the flow.
2. Use a Smart List filter "Was Sent Email".
The other best practice is just to use local assets that are cloned instead of shared assets. This way, they can also obtain program data from being in the program and are also exclusive.