Example:

‌ 1) Editor Context‌
(node:3724) UnhandledPromiseRejectionWarning: Error: Canceled
at KernelFutureHandler.dispose (D:\a\1\s\node_modules@jupyterlab\services\lib\kernel\future.js:150:31)
at _futures.forEach.future (D:\a\1\s\node_modules@jupyterlab\services\lib\kernel\default.js:875:20)
at Map.forEach ()
at DefaultKernel._clearState (D:\a\1\s\node_modules@jupyterlab\services\lib\kernel\default.js:874:23)
at DefaultKernel.dispose (D:\a\1\s\node_modules@jupyterlab\services\lib\kernel\default.js:336:14)
at DefaultSession.dispose (D:\a\1\s\node_modules@jupyterlab\services\lib\session\default.js:201:22)
at Promise (D:\a\1\s\out\client\common\utils\async.js:86:28)
at new Promise ()
at Object.callWithTimeout (D:\a\1\s\out\client\common\utils\async.js:81:12)
at JupyterSession. (D:\a\1\s\out\client\datascience\jupyter\jupyterSession.js:62:43)
at Generator.next ()
at fulfilled (D:\a\1\s\out\client\datascience\jupyter\jupyterSession.js:6:58)
at

THis is a part of jupyter session shutdown. Hard to repro and hard to get workaround.