There are two ways to assign the follow up landing page in Marketo: on the form level, and on the gated LP level.
I tend to use the LP level, as I use one form for various LPs (a best practice for scaling!)
I have recently noticed that the follow up landing pages are not being recognized when I find it in Marketo:
Everything is approved, and it just goes to our optimizely page.
Of course it works if I add the Marketo LP's external url (pages.optimizely.com/xyz).
Has anyone else come across this issue?