Are you using VBR on your cameras - it looks like the bandwidth is very close to 100% load at times - which most networks/NICs/switches cannot handle.
It looks to be the communication to the NAS which is connected trough iSCSI.
Everytime it starts to archive it shows this behaviour. It's weird thought, I would expect a constant load, not this toggling one.
The throttling is probably MTU / RSS happening due to the flood of traffic. Something is oversubscribed here, and the devices are working out how to slow it down.
If this is on your storage network, and you're using iSCSI, NFS, or CIFS, then take a look at enabling jumbo frame support from back to front- storage, switch, and server. That may make a difference in getting the data from A to B faster.
Other than that, you are looking at LACP / aggregation to up the bandwidth here. 62% is getting close to maxxing out the interface when you account for overhead in protocols and traffic.