The problem, related to the configuration of the key signature, came up late Tuesday night. The programs had difficulty downloading diagnostic keys from servers. Some of them displayed a loading screen notification that users could not reject by swiping away. Restarting the device may get rid of it, but you should not clear the storage in the app. This will not resolve the issue, and it could cause data loss and possible exposure agreements.
The programs continued to collect keys (used for contact detection) and to detect potential exposure while the problem remained active. Google engineers will work with app developers to resolve issues as soon as possible.
Google has partnered with Apple on a contact tracing system that they unveiled to public health agencies last May. However, it does not appear that the issue affected the iOS exposure notification programs.
Update 1/13 2:45 AM ET: Updated to note that Google has issued a fix.