Xref Layers Not Visible in a Viewport

Issue

The layers from one or more of your external references (Xrefs) are not visible within a viewport.

Cause

The layers may be frozen, rendering them invisible.

Solution

With the problematic viewport open, type VPLAYER in the Command line and press Enter.

You'll see several options in the Command line. Type T for Thaw and press Enter.

The layers should now be visible.