I am also seeing these kinds of messages in the server logs:
Aug 19 12:13:44 sarek jupyter-lab[429775]: [IPKernelApp] WARNING | No such comm: dfb74802b62841bc8a0d90fa226fa430
Aug 19 12:13:44 sarek jupyter-lab[429775]: [IPKernelApp] WARNING | No such comm: 6c21153a04744d7889aa1db2cf053801
Aug 19 12:13:44 sarek jupyter-lab[429775]: [IPKernelApp] WARNING | No such comm: 059f1a9957b245bcafe3bccdd6e3bc69
Aug 19 12:13:44 sarek jupyter-lab[429775]: [IPKernelApp] WARNING | No such comm: f970adf714044f668d7b84247f2576c2
Aug 19 12:13:44 sarek jupyter-lab[429775]: [IPKernelApp] WARNING | No such comm: 0860166cdb85432d943e43298bb51709
Aug 19 12:13:44 sarek jupyter-lab[429775]: [IPKernelApp] WARNING | No such comm: 9d24d011f71044a8b2bc9a93321bc0cb
Aug 19 12:13:44 sarek jupyter-lab[429775]: [IPKernelApp] WARNING | No such comm: 9bf76f444bb147368f8112b38a9ba576