error skywalking Exception while fetching data (/services) : null

[liyuntian]

We transfer the skywalking storage from one es cluster to another es cluster
if we copy all the indexes first. then start skywalking,an error was reported when opening the skywalking UI in the new cluster . skywalking Exception while fetching data (/services) : null

If we let skywalking create the index automatically, and then import the es index, there will be no errors.

What is the reason?please