Google rule ID must be allowed in ModSecurity. The login error will be logged in apache error log that your host provider can find as the following result.

[Wed Mar 06 03:26:38.152664 2019] [:error] [pid 56116:tid 139954915079936] [client xxx.xx.xx.xxx:53282] [client xxx.xx.xx.xxx ModSecurity: Access denied with code 403 (phase 2). Matched phrase "/configuration.php" at ARGS:albumid. [file "/etc/apache2/conf.d/modsec_vendor_configs/comodo_apache/08_Global_Other.conf"] [line "57"] [id "210580"] [rev "2"] [msg "COMODO WAF: OS File Access Attempt||blog.domainname.com|F|2"] [data "Matched Data: /configuration.php found within ARGS:albumid: ../../configuration.php"] [severity "CRITICAL"] [tag "CWAF"] [tag "Other"] [hostname "blog.domainname.com"] [uri "/index.php"] [unique_id "XH7bfqDDIEUYuMZ6YnW25gAAAMg"]

Please ask your host provider to allow rule_id as showing in red number, 210580 for example.