Hi,
I just checked, but the script reports a plugin version 8 releases before the current one (4.19 vs 4.20.2), please update the plugin to the latest release via the plugin manager. If the plugin is up to date, then clear all layers of cache. Also, please never revert plugin versions from newer to older ones, if you did, then in that case I recommend using a plugin wipe, and then reinstalling the plugin.
I tried to log-in to the back-end to check, but the account has no access to Ajax Search Pro options: https://i.imgur.com/4K9qc65.png
