Last week I was surprised to see that the DS apps on my Android phone weren’t able to connect to my DiskStation anymore.
I found out that the latest update to my DiskStation is to blame.
Version DSM 6.0.2-8451 broke the ability to connect to your DikStation through HTTPS for all Android DS apps, except DS Photo.
In the Synology forums people reported that disabling HTTPS/2 support solves the problem.
So in case you experience the same issue just go to Control Panel > Network > DSM Settings and disable HTTP/2 until Synology releases an update to fix this.
UPDATE: Synology released DSM version 6.0.2-8451-2 on the 6th of October. Although there is no mention in the release notes, this update solves the connection issue the Android DS apps encountered since the last DSM udpate. So go ahead an activate HTTP/2 again =)