Rtools cygheap base mismatch detected - Windows update

Question

Having used Rtools for a while on R v3.3.3 and 64bit Win10, I suddenly faced the following error when trying to locally install, i.e., compile_dll(pkg = "...", quiet = FALSE) or load_all(pkg = "...") any package via devtools:

*** fatal error - cygheap base mismatch detected

and the following suggestion in the error output:

This problem is probably due to using incompatible versions of the cygwin DLL.
Search for cygwin1.dll using the Windows Start->Find/Search facility
and delete all but the most recent version.  The most recent version *should*
reside in x:\cygwin\bin, where 'x' is the drive on which you have
installed the cygwin distribution.  Rebooting is also suggested if you
are unable to find another cygwin DLL.

None of the suggested error handling brought a solution. The concerned library cygwin1.dll was indeed only present as part of Rtools (i.e., in the Rtools folder itself).

Answer 1

Found that this was related to a recent Windows update, namely the 2017-10 Security Update for Adobe Flash Player for Windows 10 Version 1703 for x64-based Systems (KB4049179). Undoing this update under Settings/Updates and Security/... solved the issue. I would nevertheless like to know how exactly this problem arose. Beware that there are other potential issues between Rtools and Cygwin, such as "version collisions of fundamental Cygwin libraries" as described by https://www.r-bloggers.com/rtools-and-cygwin-on-ms-windows/ , but they were seemingly not related to the described problem. Also beware that any automatic Windows 10 updates can only be undone within a month of their installation.