Desktop 1.4.10 doesn't work in Debian 9 (Stretch)

I’ve been using Cryptomator on Win 10 systems with no problem, but I’d like to add it to my Linux desktop system. Unfortunately, the .appimage file that’s provided for the 1.4 tree doesn’t work on my system.

Using the KDE Plasma desktop environment.

I’ve added the appropriate file (& made a symlink so I don’t have to type quite as much to start it) in my path, and have made it executable. When I try to run it, I get a bunch of messages in the terminal window, and then the UI appears. Unfortunately, everything in the UI doesn’t respond - I can’t even use the X in the upper right to close it - I have to go back to the terminal window and cntrl-C out.

Here’s what I get:

$ ls -la /usr/local/bin
total 52880
drwxrwsr-x  2 root staff     4096 Jun  6 11:03 .
drwxrwsr-x 11 root staff     4096 Jun 20 2018 ..
lrwxrwxrwx  1 root staff       34 Jun  6 11:03 cryptomator -> cryptomator-1.4.10-x86_64.AppImage
-rwxr-xr-x  1 root staff 54139896 May  9 07:44 cryptomator-1.4.10-x86_64.AppImage

$ cryptomator
11:14:10.998 [main] DEBUG org.cryptomator.common.Environment - user.language: en
11:14:11.003 [main] DEBUG org.cryptomator.common.Environment - user.region: null
11:14:11.003 [main] DEBUG org.cryptomator.common.Environment - logback.configurationFile: null
11:14:11.003 [main] DEBUG org.cryptomator.common.Environment - cryptomator.settingsPath: ~/.config/Cryptomator/settings.json:~/.Cryptomator/settings.json
11:14:11.003 [main] DEBUG org.cryptomator.common.Environment - cryptomator.ipcPortPath: ~/.config/Cryptomator/ipcPort.bin:~/.Cryptomator/ipcPort.bin
11:14:11.003 [main] DEBUG org.cryptomator.common.Environment - cryptomator.keychainPath: null
11:14:11.004 [main] DEBUG org.cryptomator.common.Environment - cryptomator.logDir: ~/.local/share/Cryptomator/logs
11:14:11.004 [main] DEBUG org.cryptomator.common.Environment - cryptomator.mountPointsDir: ~/.local/share/Cryptomator/mnt
11:14:11.211 [main] DEBUG org.cryptomator.common.settings.SettingsProvider - Attempting to load settings from /home/davidg/.config/Cryptomator/settings.json
11:14:11.214 [main] DEBUG org.cryptomator.common.settings.SettingsProvider - Attempting to load settings from /home/davidg/.Cryptomator/settings.json
11:14:11.598 [main] INFO  org.cryptomator.launcher.FileOpenRequestHandler - Unable to setOpenFileHandler, probably not supported on this OS.
11:14:11.619 [main] INFO  org.cryptomator.launcher.Cryptomator - Starting Cryptomator 1.4.10 on Linux 4.9.0-9-amd64 (amd64)
11:14:11.813 [main] INFO  o.c.launcher.IpcProtocolImpl - Received launch args: 
11:14:12.219 [JavaFX Application Thread] INFO  org.cryptomator.launcher.Cryptomator - JavaFX application started.
11:14:12.528 [JavaFX Application Thread] INFO  o.c.ui.controllers.MainController - Unable to setPreferencesHandler, probably not supported on this OS.
^C11:14:39.199 [Thread-0] INFO  o.c.launcher.CleanShutdownPerformer - Goodbye.

The very last line (“Goodbye”) was the response when I pressed the cntrl-C to terminate the program.

Any ideas why this isn’t working under Debian, and how to get it going?