I migrated from SMF to Discourse, I did had an ad revenue decline (and visits). But currently, after almost a year I’d say I’ve recovered all my revenue, my community is more active, specially for the improved performance on mobile.
I did the migration between February and March 2018, when the steep decline shows. From there, you can see an upward trend that hasn’t stopped.
The hardest part was the reindexing of all the topics back into Google.