I've had that issue too, I can edit stuff ive made in office 2007, but not 2016, and I cant edit anything downloaded, no matter what version. I have had no issues with the ios versions, and the android versions. I hope it's a glitch, but with the recent blow to OneDrive, I do indeed think windows 10 mobile is going to be born dead, and we will see if panos can save it (crossing fingers)