Walk in freezer 404a -12 degree box temp drain line freezing and pan??

[Nix cool]

I shut down box to defrost and cleared condensate line and is insulated but keeps freezing what next?

[monkey spanners]

Is the drain line heater working and /or drain clear of blockages? If not water will back up into the drain pan. Is the fall correct on the drain line?

[Silhouette]

Is there a trap fitted? If not warm air will freeze inside the pipe!

[Coorsman777]

Try some self regulating heat tape like you would use on gutters for a house to keep them from freezing.