GA4 Realtime reporting error?

One of my four sites has, for the past couple of hours, been showing about an 80% reduction in "Realtime" traffic compared to a normal day. I checked my site and nothing has changed with regard to tag installation. Moreover, I don't seem to have lost ranking for any of my top 20 or so pages, so this is very strange indeed. Obviously, the true test will be tomorrow, when GA4 finally updates accurate traffic numbers for the whole day. For now, however, I'm feeling very panicked and unsure as to what is going on. Thoughts?