I wonder if most of these issues are on computers with Fusion Drives. The startup on my iMac is horrible, but my work laptop is an SSD-only MacBook and I don't see these problems on that one. I suspect these things occur if Spotify is not quite that "often used", so Apple keeps moving the Cache out of the SSD. It really sucks that one cannot force files onto the SSD on these Fusion drives.
Blank pages, you can click on "Liked Songs", "Artists" or "Browse" and wait 5-10 mins. It's faster to take another device and select MAC as an output device and music will play. (iMac 2019 5k, MacBook Pro 2018 13" same)