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Please have a look on UI

Can you please help share the idea.log file (select Help > Show Log in Finder) if this issue reproduces again? Thank you very much!

It looks like this is the cause:

update failed for AnAction(com.android.tools.idea.run.deployment.DeviceAndSnapshotComboBoxAction) with ID=DeviceAndSnapshotComboBox

java.lang.IllegalStateException: @NotNull method com/android/tools/idea/run/deployment/Worker.get must not return null
        at com.android.tools.idea.run.deployment.Worker.$$$reportNull$$$0(Worker.java)
        at com.android.tools.idea.run.deployment.Worker.get(Worker.java:53)
        at com.android.tools.idea.run.deployment.AsyncDevicesGetter.get(AsyncDevicesGetter.java:100)
        at com.android.tools.idea.run.deployment.DeviceAndSnapshotComboBoxAction.getDevices(DeviceAndSnapshotComboBoxAction.java:142)
        at com.android.tools.idea.run.deployment.DeviceAndSnapshotComboBoxAction.update(DeviceAndSnapshotComboBoxAction.java:394)
        at com.intellij.openapi.actionSystem.ex.ActionUtil.performDumbAwareUpdate(ActionUtil.java:176)
        at com.intellij.openapi.actionSystem.impl.ActionUpdater.doUpdate(ActionUpdater.java:378)
        at com.intellij.openapi.actionSystem.impl.ActionUpdater.lambda$null$1(ActionUpdater.java:78)

I've to report that
3. With 4 Canary 3 I see no devices in chooser and menu Run->Run does absolute nothing

does not solve this issue

This is causing canary to be unusable for ASwB users.  See bugs:
b/144865311, b/142071994

@Juan raising this to P0 because it is really critical for ASwB users.  If situation changes, please feel free to reprioritize.  

Gonna try to repro on 4.0 Canary 2. Repro steps would be useful, _especially_ for a fresh project.

Still don't have reliable reproduction steps but internal users complained and their problem was resolved with a reboot. Adapting Diglett's solution externally:

Try disconnecting all your devices and restarting ADB to see if that fixes the problem. If that doesn't work, try rebooting your computer.

Still investigating the root cause. But downgrading this to P2.

And for the record I couldn't repro with a downloaded 4.0 Canary 2 and a fresh empty activity project. Tried deploying on virtual and physical devices.

I'm looking at the logs and see:

2019-11-11 10:27:58,690 [  21328]  ERROR - plication.impl.ApplicationImpl - null
java.lang.AssertionError
        at com.android.tools.idea.run.deployment.ConnectedDevicesTask.newKey(ConnectedDevicesTask.java:129)
        at com.android.tools.idea.run.deployment.ConnectedDevicesTask.newConnectedDevice(ConnectedDevicesTask.java:107)
        at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193)
        at java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:175)
        at java.util.Spliterators$ArraySpliterator.forEachRemaining(Spliterators.java:948)
        at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:482)
        at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:472)
        at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708)
        at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
        at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:499)
        at com.android.tools.idea.run.deployment.ConnectedDevicesTask.call(ConnectedDevicesTask.java:71)
        at com.android.tools.idea.run.deployment.ConnectedDevicesTask.call(ConnectedDevicesTask.java:42)
        at com.intellij.openapi.application.impl.ApplicationImpl$2.call(ApplicationImpl.java:322)
        at java.util.concurrent.FutureTask.run(FutureTask.java:266)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at java.lang.Thread.run(Thread.java:748)

What kind of virtual device were you running? I assume that virtual devices always return nonnull AVD names. It might be better to drop those weird devices and log the errors rather than crash the whole IDE.

I use a custom emulator and I can confirm on a vanilla Emulator it is working properly with Canary 3

I guess it's somehow related to https://issuetracker.google.com/issues/137078988 and we fixed in Android Studio 3.5 with this

 -ports 5556,5559 -qemu -device virtio-net-pci,netdev=t0
 

In which version can we expect the fix ?

4.0 Canary 6

I can confirm 4.0 Canary 6 solved it. Thank you