Node-RED gives "502 Bad Gateway"

I have a few months old installation of HA on a RPi 3. Whenever I start Node-RED and click on it in the left menu, I get a “502 Bad Gateway” error. This is the log:

s6-rc: info: service s6rc-oneshot-runner: starting
s6-rc: info: service s6rc-oneshot-runner successfully started
s6-rc: info: service fix-attrs: starting
s6-rc: info: service fix-attrs successfully started
s6-rc: info: service legacy-cont-init: starting
cont-init: info: running /etc/cont-init.d/00-banner.sh
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parse error: Expected string key before ':' at line 1, column 4
[10:56:52] ERROR: Unknown HTTP error occured
 Add-on: 
 
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 Add-on version: 
 You are running the latest version of this add-on.
parse error: Expected string key before ':' at line 1, column 4
[10:57:11] ERROR: Unknown HTTP error occured
 System:   ( / )
 Home Assistant Core: 
 Home Assistant Supervisor: 
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 Please, share the above information when looking for help
 or support in, e.g., GitHub, forums or the Discord chat.
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cont-init: info: /etc/cont-init.d/00-banner.sh exited 0
cont-init: info: running /etc/cont-init.d/01-log-level.sh

Never found the error. But a fresh reinstall solved the problem.

Reinstall what? Node Red or Home Assistant?