Hello I have a very big problem and not found any solution until now. I have a site installed in a subdirectory ( A version of the main site in another language) but I am having a problem and is when I try to setup permalinks to use post name after that I get a 404 error on my pages, can’t preview posts before publishing etc. If I select plain permalink all works fine. I try everything since check the htaccess file, change permission to 666, try to rewrite the file from the wordpress backed and nothing works. This start to happens after the update of 4.9.5. The main site who is not installed in the subdirectory works fine.