WiFi Direct is to allow communication between compatible devices without using a Router - If you started to experience the issue & you changed your WiFi settings - Then yeah it's likely to be the issue 🐧
I have the same problem with my S9. Smart View stopped finding my projector after I installed the latest samsung galaxy august system update. Been trying to find a proper bug-report channel, but nobody was able to solve the issue yet. Other apps can find the projector, problem limited to Smart View and Google Home in my case. Both were working before the august update.