SUMMARY
On updating to the latest KDE Connect from Google Play, I found I could no longer access the phone's filesystem from Linux.

STEPS TO REPRODUCE
1. For a paired device, click the "Mount" button in GSConnect's menu.

OBSERVED RESULT
No filesystem is mounted.

adb logcat shows:
03-20 12:28:39.628 18591 18668 W System.err: java.lang.IllegalStateException: Could not find a valid sshd io provider
03-20 12:28:39.628 18591 18668 W System.err:    at org.apache.sshd.common.io.DefaultIoServiceFactoryFactory.newInstance(DefaultIoServiceFactoryFactory.java:67)
03-20 12:28:39.628 18591 18668 W System.err:    at org.apache.sshd.common.io.DefaultIoServiceFactoryFactory.getFactory(DefaultIoServiceFactoryFactory.java:43)
03-20 12:28:39.628 18591 18668 W System.err:    at org.apache.sshd.common.io.DefaultIoServiceFactoryFactory.create(DefaultIoServiceFactoryFactory.java:37)
03-20 12:28:39.628 18591 18668 W System.err:    at org.apache.sshd.common.AbstractFactoryManager.getIoServiceFactory(AbstractFactoryManager.java:76)
03-20 12:28:39.628 18591 18668 W System.err:    at org.apache.sshd.SshServer.createAcceptor(SshServer.java:353)
03-20 12:28:39.628 18591 18668 W System.err:    at org.apache.sshd.SshServer.start(SshServer.java:278)
03-20 12:28:39.629 18591 18668 W System.err:    at org.kde.kdeconnect.Plugins.SftpPlugin.SimpleSftpServer.start(SimpleSftpServer.java:116)
03-20 12:28:39.629 18591 18668 W System.err:    at org.kde.kdeconnect.Plugins.SftpPlugin.SftpPlugin.onPacketReceived(SftpPlugin.java:142)
03-20 12:28:39.629 18591 18668 W System.err:    at org.kde.kdeconnect.Device.onPacketReceived(Device.java:574)
03-20 12:28:39.629 18591 18668 W System.err:    at org.kde.kdeconnect.Backends.BaseLink.packageReceived(BaseLink.java:83)
03-20 12:28:39.629 18591 18668 W System.err:    at org.kde.kdeconnect.Backends.LanBackend.LanLink.receivedNetworkPacket(LanLink.java:284)
03-20 12:28:39.629 18591 18668 W System.err:    at org.kde.kdeconnect.Backends.LanBackend.LanLink.lambda$reset$0(LanLink.java:109)
03-20 12:28:39.629 18591 18668 W System.err:    at java.lang.Thread.run(Thread.java:761)
03-20 12:28:39.629 18591 18668 E SftpServer: No more ports available


EXPECTED RESULT
The user is offered a choice of filesystems shared from the phone.


SOFTWARE/OS VERSIONS
Android 7.1.1.
Fedora 29.
Gnome 3.30.
GSConnect 19 or 21.


ADDITIONAL INFORMATION
This error occurs with version 1.12.3 of KDE Connect for Android, found at https://play.google.com/store/apps/details?id=org.kde.kdeconnect_tp, but does not occur with version 1.12 found at https://f-droid.org/packages/org.kde.kdeconnect_tp/.