This is a retrospective about an incident we discovered at 9:50am PT and immediately recovered from (the incident had started at 7:57am PT).
A small subset of Tours with a specific legacy configuration  were displayed on pages that did not match the URL Rules. This resulted in Tours being erroneously displayed to users who would not have otherwise have seen the Tour. All other rules were correctly applied including Segmentation, Element matching etc. Upon learning of this issue we immediately rolled back the change and invalidated all relevant caches.
We are following up with our customers directly to provide details about how this incident impacted their Tours and Users. Please feel free to reach out for more information.
 We added support for multiple URL matching conditions (~11 months ago) and continued to support the legacy configuration of having only one URL match, when we deployed an update to how URL matching was handled the legacy configuration was omitted from the new code (and should not have been). Upon learning of this issue we immediately rolled back the change and invalidated all relevant caches.