You are not connected to any peers. There is most likely some network issue. Fix connectivity.

[rodoufu]

Parity client version: Parity-Ethereum/v2.5.1-beta-adabd81-20190514/x86_64-linux-gnu/rustc1.34.1
Parity UI version: v0.3.4 (https://github.com/parity-js/shell/releases/tag/v0.3.4)
Operating system: Linux Ubuntu 18.04.1 LTS
Installed via: deb file
Fully synchronized: no, running on dev mode as
parity --config dev --jsonrpc-apis=web3,eth,pubsub,net,parity,parity_pubsub,traces,rpc,shh,shh_pubsub,personal
Network: ethereum
I tried to restart both Parity UI and Parity Ethereum client: yes

I keep getting the error:
You are not connected to any peers. There is most likely some network issue. Fix connectivity.

[zlocate]

Please note that

Parity UI is currently only compatible with Parity Ethereum <v2.0. Read about possible alternatives here.(https://github.com/parity-js/shell#parity-ui-alternatives)