It is not rare when your blog/website has many plugins that after WordPress update, some of those plugins won’t work and will cause 500 internal error. Let’s see how to fix
To fix issue you can use undo WordPress update with backup or you can use little trick with deactivating all the plugins and activate them back one by one.
Here is how you can do it:
1. Rename plugins folder within %path_to_your_website%/wp-content to some other name, for example plugins.temp
2. Go open your website, if reason of error was plugin conflict – it must be okay now (if not only restoring from backup will help you).
3. Go to Control panel and see Plugins, there will be messages that all the plugins were deactivated.
4. Rename plugins.temp back to plugins
5. Activate plugins in Control panel one by one (bad plugin will now print message)
If nothing works: try to restore from backup