Write to SD card fails in My Cloud app on Android 5.0

I’ve just bought a 64GB micro SD so I can carry a bunch of music and photos around on my phone running Lollipop. For security reasons it is intentionally not rooted. When I try ‘Save to SD card’ having selected a track on my WDMyCloud, or having selected a track in my Downloads, I then select a folder, and it appears in the Activity log, but after a while it just fails:

I found that file managers have a similar issue, but they provide a mechanism that allows me to give permission permanently, though I have to say it was very, very obscure (Select All button while viewing the root folder - don’t get me started!).

Doing some research, I wonder if this could be something to do with changes introduced in Android 4.4 - see http://m.androidcentral.com/lollipop-brings-changes-way-your-sd-card-works-kind-youll

Any suggestions how I can get to use the nice keep-in-sync features the My Cloud app offers re. files downloaded from my NAS, but to the SD card? At the moment I am limited to the few free GB in my phone memory, and have to use a 3rd party file manager to get them onto the SD card.

P.S. A possibility related problem is that Delete in the My Cloud app Downloads folder does not remove the files from storage - it just removes them from the app, taking up space on the phone until I delete them with a file manager. Is this also a permissions thing? Maybe I should just go Apple, 'cause “it just works”, or so they say.

I am currently running Cyanogenmod 12.1 (Android 5.1) on my phone and have similar issues when my phone’s base storage is nearly full irrespective of my SD card. Are you able to confirm if this is the case for you as well by deleting some files before using the app?

Thanks for providing a possible other angle on this. I can say it’s not low on space - the WD MyCloud has 800 GB free, the phone 4 GB free, and the 64 GB SD card has 54 GB free.

I’ve come to the conclusion that the way it’s behaving is because the phone doesn’t support that size SD card and just isn’t telling me. Other apps can write files to the drive, and they can be read, but they are gone after rebooting. That doesn’t happen when I put in a 2GB card from an old phone.

Next steps are to reformat the card on a device that supports it (my Windows 7 laptop sees it as write protected, when it’s not), and to try a smaller card.

I’ll leave this post on the forum in case someone else finds they have the same problem, and can get some ideas from the things I’ve tried.

Does the saving of a file to an external SD card still occur in Android 6.1.
I have a EX2 NAS and when trying to download a file to my Android tablet from the mycloud app - it will not let me save it to the sd card, instead it fails as there is not sufficient for internal memory.

Thanks
Woody