A plenty of syslog message from influxd-systemd-start.sh Unable to gather self-signed certificate

I am using InfluxDB 2.1.1 (git: 657e1839de) on Ubuntu 20.04.3 LTS.
My /etc/influxdb/config.toml is as follows:

tls-cert = "/etc/influxdb/cert.pem"
tls-key = "/etc/influxdb/privkey.pem"

The certificate and key contains a valid Let’s Encrypt Certificate. In /var/log/syslog I receive every 10 seconds following messages:

Nov 21 00:32:05 hxx influxd-systemd-start.sh[2414]: ts=2021-11-20T23:32:05.562254Z lvl=error msg="Unable to gather" log_id=0Xwv1AZW000 error="Get \"https://hxx:8086/metrics\": x509: certificate signed by unknown authority"
Nov 21 00:32:05 hxx influxd-systemd-start.sh[2414]: ts=2021-11-20T23:32:05.565233Z lvl=info msg="http: TLS handshake error from <myip>:33738: remote error: tls: bad certificate" log_id=0Xwv1AZW000 service=http

How can I avoid this messages? How are they affected?