dygraphs hanging RStudio

[dholmesC]

Hello, starting a few days ago, simple dygraphs stopped working on my standalone Rstudio.
I do not know why. When I even run

require(dygraphs)
dygraph(nhtemp, main = "New Haven Temperatures")

Three things happen:

1. R comes back right away, but
2. nothing appears in the Viewer pane,
3. R CPU usage ramps up to 90pct (etc) until I kill the process. (I let it run for a few hours once.)

The same code appears to work fine in native R Gui. Running options(viewer=NULL) does not help.
Help .. ?

Here is a truncated setup:

[1] "1.2.5033"

$R
[1] "C:\\PROGRA~1\\R\\R-40~1.0\\bin\\x64\\R.exe"

$pdflatex
[1] ""

$bibtex
[1] ""

$gcc
[1] "C:\\STRAWB~1\\c\\bin\\gcc.exe"

$git
[1] "C:\\PROGRA~1\\Git\\cmd\\git.exe"

$svn
[1] ""

R version 4.0.0 (2020-04-24)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 10 x64 (build 17763)

Matrix products: default

locale:
[1] LC_COLLATE=English_United States.1252  LC_CTYPE=English_United States.1252   
[3] LC_MONETARY=English_United States.1252 LC_NUMERIC=C                          
[5] LC_TIME=English_United States.1252    

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

loaded via a namespace (and not attached):
[1] compiler_4.0.0 tools_4.0.0    parallel_4.0.0

SysInfo:
       sysname        release        version       nodename        machine          login           user 
     "Windows"       "10 x64"  "build 17763"  "FIBRMP6933W"       "x86-64"      "dholmes"      "dholmes" 
effective_user 
     "dholmes" 

R Version:
               _                           
platform       x86_64-w64-mingw32          
arch           x86_64                      
os             mingw32                     
system         x86_64, mingw32             
status                                     
major          4                           
minor          0.0                         
year           2020                        
month          04                          
day            24                          
svn rev        78286                       
language       R                           
version.string R version 4.0.0 (2020-04-24)
nickname       Arbor Day