Subnet mismatch causing issues - even across different networks?

I have a server on 172.23.10.14/23

The gateway is on 172.23.10.1/24

The Site (A) is summarised as 172.23/16

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Site B is 172.27/16

I have a server on 172.27.10.100/24

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The server on site B cannot access the server on Site A using SMB (well, it sort of can but then it dies after a few KB are transferred).

When I changed the subnet of the server to 172.23.10.14/24 the share came alive and worked immediately.

Why is this? Obviously you WANT the subnets to be correct, but I thought that as the networks are different from each other (even with the /23) that the server would use the gateway and all would work.

Are different devices even aware of the subnet of a peer device?