They'll normally refresh by themselves, the only normal reason they wouldn't is if you've turned off Preferences / Miscellaneous / Advanced [Troubleshooting]: no_external_change_notify.
Having Preferences / File Operations / Options / Detect external file changes on network drives turned off could also be the problem, in addition to the setting Jon mentions above.
That would stop the folders loading at all if they were remembered from a previous session, until you clicked the option to load them when you wanted to. It wouldn't stop change notifications, so it shouldn't matter here.
Are changes in those folders showing up OK in other software, or is the problem system-wide?
Have you launched the whole Opus process as admin (not just used the Admin button in Opus to elevate a single window)? That can prevent notifications from reaching Opus.
If it's only Opus that is affected, please try the suggestions and diagnostics here:
I think the problem was caused by a "true" setting in:Go to Preferences / Miscellaneous / Advanced and make sure Troubleshooting / no_external_change_notify is set to False (which is the default).