Hi Sojka,
In 4.8 the directory the logs and save games are written to moved into a UE4Game directory instead of being written to the root external directory to prevent issues with projects named the same as existing projects. Unfortunately, we discovered after release that the mkdir on some devices fails to create the intermediate directories in some cases and this means writing the files doesn’t work. There is a fix going in 4.8.2 but if you have the source form GitHub, you can apply the following patch:
https://github.com/EpicGames/UnrealEngine/commit/ae8f571047c9a0b3aff962048004bff47e40e1d9