We have the same problem using the plugin on 6 different wordpress sites. Updating and uploading plugins and themes works fine, but uploading images yields the following error:
xxx.jpeg
Unable to create directory wp-content/uploads/2017/05. Is its parent directory writable by the server?
All folders are set to 755 while files are set to 644. I have looked into the code of the plugin but I’m too unfamiliar with the workings of wordpress plugins to debug the error.