No blocks generated after about 30,000 blocks.

[beyonderyue]

System information

Geth
Version: 1.8.3-unstable
Git Commit: c754738
Architecture: amd64
Network Id: 1
Go Version: go1.10.2
Operating System: linux

Expected behaviour

generate blocks normally

Actual behaviour

After generate about 300,000 blocks, no block generated.
So I restart every node, continue generate block, but after about 600,000 blocks, no block generated again. How I debug this issue?

Steps to reproduce the behaviour

Backtrace

[backtrace]