[This is release 3.4.0, there's no Bugzilla option atm]
Starting in R 3.4.0, file.info *sometimes* returns <NA> for mtime, atime and ctime for directories. It seems to have something to do with sharing. This affects functions that use file.mtime like update.packages.
Try file.info() with a random directory. If it returns a legitimate file time, open a windows explorer window and navigate to the directory, then run the call again and it will return <NA>s.
In some cases it returns <NA>s even if the directory is not open (or in the path of an open explorer window), but this is not consistent.
Windows 10 x64, both x86 and x64 R 3.4.0; also happens on Windows 7 32-bit (not tested on Win7/64).
R version 3.4.0 (2017-04-21) -- "You Stupid Darkness"
> file.info( "c:\\windows" )
size isdir mode mtime ctime atime exe
c:\\windows 0 TRUE 777 <NA> <NA> <NA> no
R version 3.3.3 (2017-03-06) -- "Another Canoe"
size isdir mode mtime ctime
c:\\windows 0 TRUE 777 2017-04-15 10:46:50 2017-03-18 04:40:20
c:\\windows 2017-04-15 10:46:50 no
Thank you for the report, this is a known bug that has been fixed recently in R-devel (r72606).