For months now, if I leave Spotify open overnight, it will gobble up 10s of gigabytes of memory. My machine "only" has 16, so it starts swapping badly. It invariably gets to the point where macOS tells me I'm running out of disk space, which is just awful for my SSD.
Since this has been going on so long, I've been able to narrow it down to specifically the Podcasts section. I'm not sure what it is with these views, but if I avoid the Podcasts section I seem to also avoid the memory leak.
I know a memory leak for the macOS client was recently fixed, but this occurred just last night, Jan 9th 2019. After reopening Spotify, I confirmed that my Spotify version is 184.108.40.206.gf6bc1b6b, which should contain that fix.