Complex plugin conflict

This morning one of my team members send me a message with a fatal error when he tried to access the wp-admin panel.
By reading the error status, it was shown in the wp-smush plugin. So I've uninstalled it via the hub, and again I've got the same kind of error with wp-defender.
I asked but nobody seems to have done a manipulation on the website between yesterday 18h and this morning.
Same manipulation with Defender, and again the same error. And the wp-admin page showing an error 500. So I've backed up all the plugin, with a backup from yesterday at 12h. But the error is still there.
WP admin page is showing an error 500 when some of the plugins are activated at the same time (YOAST SEO, WP Smush, WP Cost Estimation & Payment Forms Builder, Defender).