I think I have found the problem, it's related to multisite environments only.
To fix the issue, please replace the file contens in wp-content\plugins\ajax-search-pro\includes\classes\actions\class-asp-indextable.php with this: https://gist.githubusercontent.com/anag0/25d119fb40fd1a4ea3d44b6e82822416/raw/5cb9e43bb5bae759ccf5bc10180c638c1f151095/class-asp-indextable.php
After that, make sure to re-create the index table under the Index table options submenu. That should solve the issue permanently. I will also make sure to include this fix in the next release.
PS: please have a back-up of everything, before making any direct changes.Best,
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