Having an unlocked bootloader fails SafetyNet which Snapchat must pass to login. Back in v18 of magisk this was properly taken care of and would be forced to pass with the Hide feature.
Magisk dev since March 2019, no longer cares about the Hide feature they promote so heavily(but an app with over 1 billion downloads is classified as a "minor app" that the dev has no interest in maintaining proper hiding code for).
The only option is to have a fully stock ROM from Google's download site or OTA,unrooted and a locked bootloader to pass safetynet if you are interested in using Snapchat in 2019.
No other options exist
Has anyone tried running snapchat through island?