One of the sites I maintain is still on PHP 7.1.33 (already waiting 2 years for the correct Plesk credentials) and it appears to give an error after the installation of 4.3 beta 1: Een fout van het type E_PARSE werd veroorzaakt op regelnummer 568 van het bestand /.../wp-content/plugins/mainwp-child/class/class-mainwp-child-actions.php. Foutmelding: syntax error, unexpected ')'
I think it’s because of the trailing comma after the last parameter in line 567 which isn’t supported yet in PHP 7.1.