We have a tracking issue for Router crashes when Kubo is being used · Issue #9998 · ipfs/kubo · GitHub it contains two workarounds you should try.
It would help us if you could also comment a report on the issue 
We got a very similar report here IPFS in Brave slows internet speeds to a crawl
About why it does that, this is normal this is the DHT provide process, your node is storing itself in all the CIDs you are creating inside the Distributed Hashed Table. This is a big decentralised phone book that contains a map of CID → List of nodes hosting it and Node → IP + PORT + Protocol list
You can enable accelerated DHT client https://github.com/ipfs/kubo/blob/master/docs/config.md#routingaccelerateddhtclient, however it is extremely bursty, overall it makes multiple order less connections and is a few hundred thousands times faster, but in a short time bursty.