Just upgraded from my 5 year old iPhone 6 to the Galaxy S10 and have now found myself here because of the same issue as everyone else. Swipe down to search within Liked Songs and Playlists was perfectly present and functioning on my iPhone and I used it a lot, it's absurd to see it's not there on a brand new flagship device and sad to see that this issue has been going on for a while with no action taken.
Still unable to search via the playlist after a full year of complaints.
I was sad to see this forum confirm all of what I already knew, seeing as how my partner has an iPhone as has been able to search without issue. I don't understand why it was removed, and no one in the Android community knows either. I have been using Spotify since before my partner (the iPhone user) and even introduced him to it. I've been a premium user, on and off for the betterment of 7 years and definitely have a loyalty to Spotify. This, however, is egregious, and will eventually lead me to want to search for other options for a service. Playlists be d*mned, I will rebuild elsewhere.