The Switch 4.0.0 system update rolled out recently and after just a few days there have been reports that it caused a lot of bugs and issues for users in Japan. Some users reported that they lost sound on TV after the update, some had joycon issues and even a resolution change on their TV.
— ふわ (@fuwa_saaya_) October 19, 2017
Report suggests that there is no sound on the TV after the update
— MASA (@MASA_T_O) October 19, 2017
HDMI input issues.
— ミティア (@metear3520) October 19, 2017
This user reports a resolution drop from 1024 × 768 to 848 × 480 on TV.
— あくあ (@aqua_felis) October 19, 2017
A system boot error after the update. It was bypassed by removing the SD card during the boot process.
There are also reports in the switch subreddit like this one with another sound issue after the 4.0.0 update. Nintendo is yet to respond to these reports.