Error 4042 using config_sync

Customer has configured a pair of maxscale instances using `config_sync`. They are `maxscale-blue` and `maxscale-green` using the following steps:

• `systemctl stop maxscale` on `blue`
• `rm /var/lib/maxscale/*.json` to make sure the only config it will load is what is in the config files (both hosts have `persist_runtime_changes` and `load_persistend_configs` set to FALSE)
• `systemctl start maxscale` on `blue`
• Set one of the nodes to maintenance mode to trigger a config change and verify a new config is written to the database
• `systemctl stop maxscale` on `green`
• Update `/etc/maxscale.cnf` to be identical to what is configured on `blue` and similarly run `rm /var/lib/maxscale/*.json`
• `systemctl start maxscale` on `green`

Looking at the logs on `green`, the following warning is logged approximately every 5 seconds:
warning: (ConfigManager); Failed to update node state to 'OK' for hostname 'maxscale-green': Query 'UPDATE maxscale_config SET nodes = JSON_SET(nodes, CONCAT('$.', JSON_QUOTE('maxscale-green')), 'OK') WHERE version = 1 AND cluster = 'mariadb-monitor'' failed. Error 4042: Syntax error in JSON path in argument 2 to function 'json_set' at position 12.

The hostname is "maxscale-green".
Here are the config_sync parameters:
config_sync_cluster=mariadb-monitor
config_sync_db=db_admin
config_sync_user=maxscale
config_sync_password=REDACTED

Running `SELECT VERSION();` on the backend DB shows "MariaDB 10.11.1-MariaDB-1:10.11.1+maria~ubu2004-log".

The Maxscale user's grants are as follows:
GRANT SELECT, INSERT, UPDATE, CREATE ON `db_admin`.`maxscale_config` TO `maxscale`@`%`;

No errors found in the logs for `blue`. Both hosts are successfully handle client SQL queries.