Kubernetes cluster 1 year ago stopped working

Hi! I do install Kubernetes cluster 1 year ago (1.11; 11.08.2018 Ubuntu 18 server,One Master one worker)
25 day ago I noticed that soon end PKI. I updated cluster to 1.12 and 1.13.2 version. I saw PKI validity was 2020. But today 12.08.2019 stopped working. Exactly one year after the start. “What kind of mine?” Can I fix it?