I have installed ELK in my Ubuntu-18 server and configured Kubernetes cluster with filebeats.
Few days ago, Kibana -> Logs were showing logs. But now I can not see any log shown there.
I had checked kibana and elastic status. They had no errors also filebeats doesnt have errors.
@sachithmuhandiram
that can be a lot of things 
I'd first start with checking if your data is axctually getting indexed. Run a query against Elasticsearch directly (e.g. in Kibana dev tools, something like GET /filebeat*/_search. Does it show your data?
Also make sure that the time-range in Kibana correctly captures the timerange of your data. Easiest way is to go to Discover and check there.