If you are hosting your site with Siteground you will need to contact them and ask them to re-add the rule for Search bar.
A false-positive alarm with the mod_security rules causes the module to malfunction. What these rules do is filter all of the requests that come to your site. It is a set of rules with regular expressions that helps to instantly ex-filtrate the commonly known exploits. Modsecurity obstructs the processing of invalid data (code injection attacks) to reinforce and nourish server's security. However, false-positive alarms are also possible. These rules will need to be whitelisted on Siteground in order for PixSearch to function properly.