What is a configmap cache?
From the docs here
The kubelet uses its local cache for getting the current value of theConfigMap from Kubernetes API Server. The type of the cache is configurable using theConfigMapAndSecretChangeDetectionStrategy field in theKubeletConfiguration struct. A ConfigMap can be either propagated bywatch (default), ttl-based, or simply redirecting all requestsdirectly to the API server. As a result, the total delay from themoment when the ConfigMap is updated to the moment when new keys areprojected to the Pod can be as long as the kubelet sync period + cachepropagation delay, where the cache propagation delay depends on thechosen cache type (it equals to watch propagation delay, ttl of cache,or zero correspondingly)
failed to sync configmap cache could be because kubelet could not connect to Kubernetes API Server to get the updated configMap data. I would look into Kubelet logs using journalctl -u kubelet