For anyone who's on Hostinger and using WP Umbrella (and possibly other 3rd party services).

Yesterday evening, Hostinger automatically turned on their CDN on all of my Hostinger-based sites. Following that, WP Umbrella had problems syncing, was giving false 503 alerts and showing other issues. After an hour+ of troubleshooting, I tracked the root cause back to Hostinger's CDN. After disabling it, WP Umbrella is running fine again.

I'll be reporting this to both Hostinger and WP Umbrella, but wanted to give the community a heads up here, as well.