Tested on an AMD A4-6300 CPU running Windows 10 Pro build 1703 and on 2 Minecraft Windows 10 editions, same results.
RAM: 4GB
GPU: Radeon HD 8370D

Bug Description
During random gameplay on online servers (PigRaid, etc) opening the chat window eventually locks up and freezes Minecraft W10 edition, along with the PC. After loading task manager and Minecraft W10 edition side by side, Minecraft continuously fills up the ram, from 600MB to almost 2GB when the chat bug is happening. The only way to stop it is to be fast enough to end Minecraft Win10 process on task manager, or rebooting win10 through a hard reset (Hard reset, aka pulling the power)

Keep in mind, there is no reliable way to reproduce this bug. But when it does happen (which it does frequently on this PC) it may possibly a game-breaking bug as it prevents the player from being immersed.