'plot/vglt' is from version 1 plotting. Version 2 uses 'plot/vega'. If you're seeing VGLT in the ASDF file it means that it's the old version, and you'll need to pull in the source for a manual install from github until Quicklisp gets updated. The systems you'll need are:
- alexandria+
- data-frame
- dfio
- lisp-stat
- plot
- numerical-utilities
- select
- sqldf
It may be easier to get help from one of the community resources [1] (StackOverflow, github issue/discussion, mailing list) than HN, as those are always monitored.