Thank you for your efforts.
After asking for your help I continued checking a solution.
The “SiteGround Security” Version 1.1.2 plugin was affecting Lawyer Zone Pro 3.0.2 theme.
I had only kept “SiteGround Security” plugin on, because SiteGround are my hosting company’s own plugin.
I guess, I will have to find a security plugin that is compatible with Lawyer Zone Pro 3.0.2 theme for protection against brute-force attacks, compromised login, data leaks etc.
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SiteGround Security Version 1.1.2 – https://www.siteground.co.uk/blog/sg-security/