Why is the Algolia index population process with Search Plus timing out?
Trying to get property of non-object on line 519 of /craft/plugins/searchplus/services/SearchPlus_AlgoliaService.php


That sounds suspiciously like a bug in the plugin to me.  I'd recommend contacting the plugin's author and reporting it to them for further debugging:

https://transition.topshelfcraft.com/software/craft/searchplus/faq/how-can-i-get-support