Hello,
It seems the directory xenial-cran40 is missing from the RStudio CRAN mirrors (both Ubuntu Packages For R - Brief Instructions and Ubuntu Packages For R - Brief Instructions). Though it has been available from the origin Ubuntu Packages For R - Brief Instructions and other mirrors for at least 10 days or so.
Origin:
RStudio CDN mirror:
Could someone please look into this discrepancy?
Thanks!