"RS-7445 [Serv CELLSRV hang detected] [It will be restarted]          "
"A kernel crash has caused the system to reboot."
This ended up to be related to bug 25374245.
The workaround is to monitor the cell offload server resident memory and manually restart it before it gets above 40 GBs.
You can do this in rolling mode using below commands:
cellcli -e list griddisk attributes name,asmmodestatus,asmdeactivationoutcome
cellcli -e alter cell restart services cellsrv;
More information can be found in below MOS note:
Exadata Cell Node Crashed with memory starvation (Doc ID 2421920.1)