Clients don't reconnect after power failure

Our Ignition Gateway (7.9.13) runs on a VM and 400 clients are connected to.

Yesterday, the plant was in production when a power failure occurred.
About 375 clients lost power at the same time.
When the power recovered, we let 20 minutes to the client to reconnect but only 10 clients succeeded to connect. The others show the Client Launcher window

We decided to Restart the Gateway because we thought the clients cannot be able to connect to it.
After the restart, nothing happened. Clients still not connected.
We had to relaunch the application of the 350 unconnected clients.
Can you help me to avoid doing this one more time?