Here is a somewhat unordered list of additional resources that could help you learn multiplayer or just serve as additional little bits and pieces.
Blog Posts and Websites
Posts by Wizardcell
Posts by Vori (Vorixo)
- Multicast/Client RPCs vs OnReps (towards stateful replication)
- How to replicate thousands of Actors efficiently (network managers)
- A better and non-destructive synced network clock
- Understanding replication atomicity (why you need NetSerialize on some critical structs)
- Rewinding in Multiplayer
Posts by KaosSpectrum
- Experimental: Sample Code for implementing Instance Replays
- Sequence Diagram of the Character Movement Component
- Custom Struct Serialization for Networking in Unreal Engine
- Unreal Engine Improvements for Fortnite: Battle Royal
- Finding Network Exploits
- Twitter Post by Michael Noland (@joatski) - Check if Server or Client caused a Breakpoint in C++
- Online Beacons UE Docs
- Online Beacons Tutorial with Blueprint Access
- What are Online Beacons and how do they work?
- Party Beacon - How does it work?
Videos and Channels
- Multiplayer in Unreal Engine: How to understand Network Replication
- UE4 - Advanced Networked Movement Tutorial (Sprinting & Wall Running)
- Network Multiplayer Fundamentals | Live from HQ | Inside Unreal
- Replication Graph for Optimizing Real-Time Strategy Games | Unreal Fest Europe 2019 | Unreal Engine
- Replicating Chaos: Vehicle Replication in Watch Dogs 2
- Deterministic vs Replicated AI: Building the Battlefield of "For Honor"
- Network Scripted Weapons and Abilities in "Overwatch"
- Overwatch Gameplay Architecture and Netcode
- I Shot You First: Networking the Gameplay of Halo: Reach
- It IS Rocket Science! The Physics of Rocket League Detailed