Here are some workaround for this issue:
1. Check first if this is only happening in Apps Manager. Use the cf cli to get details on the "Unknown" services and run cf service <service-name> and check for successful response

2. Check if the service offering can be seen in marketplace. cf target -o org -s space where the Unknown service resides then do cf marketplace. You notice that the Redis Service Offering is not shown

3. The issue is caused when a service offering is disabled. You can resolve this by
cf enable-service-access -b broker -p plan -o orgNote: As of Tanzu Application Service version 4.0.8 and prior versions does not contain a fix. A bug fix story has been opened and waiting to be assessed.