Settings > Battery > App launch > find Safe Lagoon > deactivate "Manage automatically" and set all three options active (Auto-launch / Secondary launch / Run in Background)

Settings > Battery > check that Power Save Mode is disabled (and any other battery saving mode)

Settings > Apps & notifications > Apps > find Safe Lagoon > Battery > disable Power-intensive prompt

Tap the Overview button to open a list of recently used apps > find Safe Lagoon > tap the "lock" button