Same problem here with LG G3, Android 5.0, 64GB Sandisk Ultra SD Card: Can not delete files on SD Card, after the "grant access" dialog. Tried many times without success. After setting the access for the SD Card in the grant access dialog, its just not working. BUT: switched to an old 16GB SD Card, formatted inside the G3 and after the "grant access" dialog everything works. The problem is, that the 64GB SD Card is getting formatted in exFAT format, while the 16GB SD Card ist getting formatted in FAT32. The difference between working and not working is the file system. The exFAT is a modern version of the FAT file system with file system permissions (ACL) included. It seems, that Poweramp (current version 2.0.10) can not handle this. Other applications (i.e piktures) do not have this problem, so its not a general G3 problem.