Google Drive authentication - if you have issues authenticating with Google Drive, please ensure Chrome browser is installed and it is the default browser. Also try with custom Chrome tab option on account screen. If issue persist try clearing data for Chrome browser in Android App settings. Firefox has also been reported by some users to work. Simple browsers on app store that use an internal standard WebView with not be able to work with the security measures Google is enforcing.
Instant sync issues - on Android 6.x/7.x instant sync functionality will not work for most devices for external SD card. This is an Android bug or perhaps a new undocumented limitation by Google. Nothing we can do about it unfortunately.
Writing to external SD card - if you are using a newer version of Android and have issues writing to external SD card please see here for more info.
Bad request errors or failing folderpairs - please try to re-authenticate account. In some cases you also need to re-select to remote folder for folderpairs, since the path structure on the remote end has changed because of usages of new API versions. Just re-select the folder you are already using, so the remote folder info can be refreshed.
OwnCloud connections issues may be caused by streamlining of the configuration into two account types for ownCloud 6⁄7 and 8 respectively. Please reconfigure your accounts accordingly. If you get something like “refused stream” error for HTTP/2 you need to upgrade to latest nginx web server and version 2.9.4, where this is fixed.
OwnCloud upload issues may be caused by incomplete account configuration. Make sure you specify the correct protocol in server name field, either HTTP or HTTPS - this should match the server endpoint. If your server redirects HTTP to HTTPS, this will not always work for uploads for example, so make sure this configured correctly
HTTP connection errors can happen on newer Android devices, since deprecated encryption ciphers are no longer enabled by default with OkHttp/Android to increase security. This means, if you are connecting to an insecure web server using WebDAV or ownCloud, the connection may fail. You can either upgrade your server or try to enable self-signed certificates for you WebDAV/ownCloud account. Se here which protocols/ciphers are supported on which Android versions: https://developer.android.com/reference/javax/net/ssl/SSLEngine.htm