Proxmox XL710 MIkrotik CRS354-48P-4S+2Q+RM

I have a server with a lan board based on XL710 with a 40GB connection to a Mikrotik CRS354 and a second 10Gb connection.
The 2 lan ports are in the same bridge, but when I disable on the switch the 10GB connection, I realize the 40GB is not working.
On the Mikrotik the 40GB DAC cable is properly recognized.
The 40GB port is seen as 4 10GB ports; if I try to make a bond is not working, if I leave the ports separate, only the first has trafic.
Someone can help me?

The 40GB on the 354 will always show all four ports, but only the first one will link up. You can leave the other three alone. You may have to set the FEC mode on the first one if it doesn’t show a link at 40Gbps on the Ethernet stats.

Thank you for your answer. It seems working properly now.

Is it normal that if I change anything in the settings, I loose the connection for a certain time?

It depends on the setting. Changes involving the bridge generally, as well as the port you are using to connect to the switch, can both affect reachability of the switch while It resets STP and relearns MAC addresses.