CPU usage spiking to 100%, regardless of the plugin

When plugins are enabled, CPU usage spikes to 100%. The plugin doesn't seem to matter. It happens with multiple plugins. Raw access logs are showing a lot of failed requests for /wp-includes/js/jquery/jquery-migrate.min.js?ver=1.4.1 from WordPress itself, but the site seems to function correctly.
JS Console does show 404 for /wp-includes/js/jquery/jquery-migrate.min.js?ver=1.4.1 but the file exists. The debug.log shows nothing relevant or any errors.