So, Fedora 26 is out. And with it comes a new openssl which is ABI incompatible with some programs. Turns out one of those is Rstudio. I presume the people at Rstudio are working on migrating to the new openssl. But in the meantime you may want to use Rstudio on F26.
If you are on Fedora 26, you will need to install the compat-openssl-devel package.
This will delete openssl-devel, but you can re-install it later after Rstudio is built. If you are building it for the first time, there are some instructions here.
If you migrated from F25 you should update all your plugins from within Rstudio as recommended in a prior post.