Recording didn't import from Garmin
If your recording hasn't synced from Garmin Connect to Slopes, there's a couple of things to check.
Activity Profile
If you don't record with Garmin's skiing/snowboarding activity profile then your data will not be imported into Slopes.
If you're not sure if your watch has this functionality, you can check on their website. Pick your product → Specs → scroll down to "Outdoor Recreation". If you can use it for skiing/snowboarding, these activities will be listed in "Available Outdoor Recreation Profiles". Alternatively you can look up your device's details via their support center.
Activity Type
The activity type should be "Resort Skiing or Snowboarding" as below:
Privacy Settings
Some users have reported that their recordings aren't syncing if their privacy settings are set to "Only Me". If this is the case, changing your privacy settings to "My Connections" then disconnecting and reconnecting your Garmin Connect account in Slopes via the Account tab → Online Integrations → Import from Garmin should get things working.
This help article explains how to change privacy settings.