Kubernetes flannel pod getting the wrong network
You have either a bad understanding or misconception about how a cidr works.

10.105.5.128/21 is just one address in the range 10.105.0.0 - 10.105.7.255.
So either your cidr bits are not the one you're expecting, 10.105.5.128/26 would be a valid network definition but that's a /26 subnet within the 10.105.0.0/21, or you're not using the proper network definition.

You can check those division on this very helping site (the link already use your networks above.