@damianos
Could you please let me know exactly what steps you took before the site went down? Was it as simple as updating the plugin within the WordPress Admin > Updates screen?
Would you be able to tell me what do you have in the settings page for “Delete FULLTEXT indices on uninstall” and “Delete FULLTEXT indices on deactivate”. Are these enabled or disabled. Please can you disable them before upgrade.
I also think we might need to try a different approach to the upgrade. i.e. manually and ideally if you’re in a position to try this out on a staging site. Would that be possible?
In either case, what I’d like to try is downloading the plugin: https://downloads.www.ads-software.com/plugin/contextual-related-posts.zip
Then going to Plugins > Add New > Upload and selecting the file you’ve downloaded. It should prompt you to replace the plugin showing you the old (3.4.2) and this new 3.5.0 version. If this still gives you the issue, I assume you might have access to file manager on your dedicated server. If so, the easiest way then to disable the plugin is to go to /wp-content/plugins/ and rename the contextual-related-posts folder. We might need to look at other changes if that still gives an issue, including disabling Freemius manually in the code.