Can you verify the shards?
curl -s http://localhost:9200/_cat/shards?pretty
You can also check the browser console: As the error shows up in Kibana and therefore in the browser, opening the browser console (F12) helps to show additional information. Inside the json-formatted response , failures are quite nicely listed for each shard. And more importantly: The reason why the shard(s) failed appears, too.
So the way to isolate this problem would be for you to figure out which visualization is giving you this error.
Can you please add your visualizations one by one and open your logs- both Kibana logs and dev browser logs and check if there are any error messages?
Also did you make sure - you checked if there were any reindexing needed to be done for your index pattern and saved objects to ensure they worked ok in previous version?
Unfortunately , at this point am not sure how to customize the error/warning message . Am tagging @timroes - when he has time, he will answer this question .
Thanks
Rashmi