plot.loadReg doesn't produce full set of diagnostic plots

[jsta]

If I run the example from the docs:

data(app1.calib)
app1.lr <- loadReg(Phosphorus ~ model(1), data = app1.calib, 
                       flow = "FLOW", dates = "DATES", conc.units="mg/L",
                       station="Illinois River at Marseilles, Ill.")
# Produce the full suite of diagnostic plots
plot(app1.lr)

I get an Observed vs. fitted plot but none of the remaining plots. Instead I get an error:

Warning message:
In device(width = width, height = height, pointsize = fontSize, :
Quartz device is not available on this platform

platform details

 setting  value                       
 version  R version 4.0.3 (2020-10-10)
 os       Ubuntu 20.04.1 LTS          
 system   x86_64, linux-gnu           
 ui       RStudio                     
 language (EN)                        
 collate  en_US.UTF-8                 
 ctype    en_US.UTF-8                 
 tz       America/New_York            
 date     2021-01-18 

[jsta]

I can get the other plots if I manually specify the which argument (e.g. plot(app1.lr, which = 2)).