Custom fields as well as customisations to layouts made via Studio to the Campaigns Edit view prior to the latest versions upgrade are ignored by the new campaigns wizard (but they are still present in Studio).
In order to recover them I had to modify the files:
modules/Campaigns/WizardNewsletter.php
and modules/Campaigns/tpls/WizardCampaignHeader.tpl
For me this is a bug because those fields as well as the layouts shouldn’t be lost with the new Campaigns wizard.
Similarly I have edited modules/Campaigns/WebToLeadCapture.php to reimplement a functionality that I had added when someone fills a form from a web to lead form (although I already knew that this last modification would not have been upgrade safe).
The functionality is a list of email addresses to be notified by email when someone fills a web to lead form.