Ispconfig is not syncing data to other server (mirror setup)

Hi,
I'm having issues with ISPConfig not synchronizing data through my mariadb galera cluster.
My setup:
server 1: web + db + mail
server 2: web + db + mail
server 3: db

ISPConfig is installed on server 1 and 2 where server 2 is configured as a mirror of server 1.
On server 1 ISPConfig has been installed as a master and server 2 has been added as a slave.
I made sure I used different names for the databases (dbispconfig1 / ispconfig1 vs dbispconfig2 / ispconfig2).

At first I added a domain for my email.
I was able to see this on dbispconfig1 (server 1) and on dbispconfig2 (server 2).
Now I tried to add a new domain but I can only find it back on server 1 in dbispconfig1.
Is there any logging where I can see what's going wrong?

The database is using innodb.

Linux distro: Ubuntu 16.04.2 LTS
ISPConfig version: ISPConfig 3.1.2

Config of the galera cluster on server 1:
[mysqld]
binlog_format=ROW
default-storage-engine=innodb
innodb_autoinc_lock_mode=2
#bind-address=0.0.0.0
#bind-address=192.168.151.36
bind-address=192.168.164.8

# Galera Provider Configuration
wsrep_on=ON
wsrep_provider=/usr/lib/galera/libgalera_smm.so

# Galera Cluster Configuration
wsrep_cluster_name="db_cluster1"
wsrep_cluster_address="gcomm://192.168.151.36,192.168.170.39,192.168.144.28"

# Galera Synchronization Configuration
wsrep_sst_method=rsync

# Galera Node Configuration
wsrep_node_address="192.168.151.36"
wsrep_node_name="webdb01a"


##### SERVER #####
IP-address (as per hostname): ***.***.***.***
IP-address(es) (as per ifconfig): ***.***.***.***, ***.***.***.***, ***.***.***.***, ***.***.***.***
[WARN] ip addresses from hostname differ from ifconfig output. Please check your ip settings.
[INFO] ISPConfig is installed.

##### ISPCONFIG #####
ISPConfig version is 3.1.2


##### VERSION CHECK #####

[INFO] php (cli) version is 7.0.15-0ubuntu***.***.***.***

##### PORT CHECK #####

[WARN] Port 21 (FTP server) seems NOT to be listening

##### MAIL SERVER CHECK #####


##### RUNNING SERVER PROCESSES #####

[INFO] I found the following web server(s):
Unknown process (haproxy) (PID 1207)
[INFO] I found the following mail server(s):
Postfix (PID 6837)
[INFO] I found the following pop3 server(s):
Dovecot (PID 6894)
[INFO] I found the following imap server(s):
Dovecot (PID 6894)
[WARN] I could not determine which ftp server is running.

##### LISTENING PORTS #####
(only ()
Local (Address)
[localhost]:10025 (6837/master)
[localhost]:10026 (9168/amavisd-new)
***.***.***.***:3306 (1747/mysqld)
[localhost]:10027 (6837/master)
[anywhere]:587 (6837/master)
[localhost]:11211 (3460/memcached)
[anywhere]:110 (6894/dovecot)
[anywhere]:143 (6894/dovecot)
***.***.***.***:1936 (1207/haproxy)
***.***.***.***:80 (1207/haproxy)
***.***.***.***:8080 (1207/haproxy)
[anywhere]:8081 (11862/nginx)
[anywhere]:465 (6837/master)
***.***.***.***:8084 (11862/nginx)
***.***.***.***:8085 (11862/nginx)
***.***.***.***:8086 (11862/nginx)
[anywhere]:22 (3514/sshd)
[anywhere]:4567 (1747/mysqld)
[anywhere]:25 (6837/master)
***.***.***.***:443 (1207/haproxy)
[anywhere]:993 (6894/dovecot)
[anywhere]:995 (6894/dovecot)
[localhost]:10023 (3805/postgrey.pid)
[localhost]:10024 (9168/amavisd-new)
*:*:*:*::*:10026 (9168/amavisd-new)
*:*:*:*::*:587 (6837/master)
[localhost]10 (6894/dovecot)
[localhost]43 (6894/dovecot)
*:*:*:*::*:8081 (11862/nginx)
*:*:*:*::*:465 (6837/master)
*:*:*:*::*:22 (3514/sshd)
*:*:*:*::*:25 (6837/master)
*:*:*:*::*:993 (6894/dovecot)
*:*:*:*::*:995 (6894/dovecot)
*:*:*:*::*:10023 (3805/postgrey.pid)
*:*:*:*::*:10024 (9168/amavisd-new)




##### IPTABLES #####
Chain INPUT (policy ACCEPT)
target prot opt source destination
f2b-sasl tcp -- [anywhere]/0 [anywhere]/0 multiport dports 25,465,587,143,220,993,110,995
f2b-ReqLimit tcp -- [anywhere]/0 [anywhere]/0 multiport dports 80,443
f2b-nginx-http-auth tcp -- [anywhere]/0 [anywhere]/0 multiport dports 80,443
f2b-ssh-ddos tcp -- [anywhere]/0 [anywhere]/0 multiport dports 22
f2b-ssh tcp -- [anywhere]/0 [anywhere]/0 multiport dports 22
f2b-mysqld-auth tcp -- [anywhere]/0 [anywhere]/0 multiport dports 3306
f2b-dovecot tcp -- [anywhere]/0 [anywhere]/0 multiport dports 25,465,587,143,220,993,110,995
f2b-postfix tcp -- [anywhere]/0 [anywhere]/0 multiport dports 25,465,587
f2b-pure-ftpd tcp -- [anywhere]/0 [anywhere]/0 multiport dports 21,20,990,989
f2b-php-url-fopen tcp -- [anywhere]/0 [anywhere]/0 multiport dports 80,443
f2b-sshd tcp -- [anywhere]/0 [anywhere]/0 multiport dports 22
DROP tcp -- [anywhere]/0 [anywhere]/0 tcp flags:!0x17/0x02 state NEW
DROP all -f [anywhere]/0 [anywhere]/0
DROP tcp -- [anywhere]/0 [anywhere]/0 tcp flags:0x3F/0x3F
DROP tcp -- [anywhere]/0 [anywhere]/0 tcp flags:0x3F/0x00

Chain FORWARD (policy ACCEPT)
target prot opt source destination

Chain OUTPUT (policy ACCEPT)
target prot opt source destination

Chain f2b-ReqLimit (1 references)
target prot opt source destination
RETURN all -- [anywhere]/0 [anywhere]/0

Chain f2b-dovecot (1 references)
target prot opt source destination
RETURN all -- [anywhere]/0 [anywhere]/0

Chain f2b-mysqld-auth (1 references)
target prot opt source destination
RETURN all -- [anywhere]/0 [anywhere]/0

Chain f2b-nginx-http-auth (1 references)
target prot opt source destination
RETURN all -- [anywhere]/0 [anywhere]/0

Chain f2b-php-url-fopen (1 references)
target prot opt source destination
RETURN all -- [anywhere]/0 [anywhere]/0

Chain f2b-postfix (1 references)
target prot opt source destination
RETURN all -- [anywhere]/0 [anywhere]/0

Chain f2b-pure-ftpd (1 references)
target prot opt source destination
RETURN all -- [anywhere]/0 [anywhere]/0

Chain f2b-sasl (1 references)
target prot opt source destination
REJECT all -- ***.***.***.*** [anywhere]/0 reject-with icmp-port-unreachable
RETURN all -- [anywhere]/0 [anywhere]/0

Chain f2b-ssh (1 references)
target prot opt source destination
RETURN all -- [anywhere]/0 [anywhere]/0

Chain f2b-ssh-ddos (1 references)
target prot opt source destination
RETURN all -- [anywhere]/0 [anywhere]/0

Chain f2b-sshd (1 references)
target prot opt source destination
RETURN all -- [anywhere]/0 [anywhere]/0