Other
Quality of Service
A look at common router functionality
Many routers have a "Quality of Service" feature. This attempts to prioritise 'urgent' traffic, such as voice chat and gaming. This prioritisation comes at the expense of less urgent traffic such as web browsing and file downloads.
Although QoS should - in theory - help Path of Exile, it necessitates the router processing your internet traffic rather than forwarding it as soon as possible. Additionally, if your router fails to categorise Path of Exile-related traffic as gaming - perhaps due to relying upon a whitelist - the game could be placed in the "slow lane" created by the feature.
Consider disabling
Quality of Service so your traffic is as consistent and predictable as possible.