Hi @J Fowler
Here are few documents that give the complete Troubleshooting guide for Azure Redis Cache
Server side patching definitely has a effect as explained in one of the document above.
Please go through these and check if these help and the application should be prepared for patching outages and the document explains the same. If that is not possible, the right way forward is to contact support and work with them regarding the Failover error type.
Hope this helps.