First off there are issues with playing music where it will play the same song over and over again even though repeat is off; also sometimes when you play a song it will play a different song like the song right before the one you selected or sometimes it will even crash the app when trying to play a song.
Next would be how images are being displayed, they show up small instead of maximized which is how it should be and use to be, i don't know why you guys changed that!? The displaying of gifs would be an amazing improvement as well, I've wanted this for quite some time now.
Lastly some videos do not play or get distorted in visuals and audio, happens mostly with the flv format which leads me to the next thing which is more support for different formats and better optimization in general when playing a video.
This app is really amazing and i like it more than any other personal cloud service, though these issues have sent me looking for alternatives (unsuccessfully). Younity is a good example while every issue i mentioned is fixed in there app and there UI/theme is very likable, the way it syncs files is terrible and doesn't let you know when it is done scanning everything. After a day of letting it scan all the files when i try to access basic stuff like music, photos and videos they will lag terribly or not play certain files at all as if it never synced them. On top of all of that to access crucial features like using the app remotely you have to pay for their subscription which is way overpriced, especially when you guys offer these services for free. If you fixed these issues, i would gladly pay $5-10 if all sudden you guys wanted to charge for your app.
Anyways thanks for taking the time to read this and i hope you will consider my recommendations.

-Alice
Edit: btw i use the iPhone 6 Plus and have used your app on all of the past IOS versions since the last Tonido update, i am currently on IOS 11 Beta 7.