Please describe the problem you are having in as much detail as possible:
On Master the GuildChannel properties for messages are missing! It is fine on Stable and for other channels types but missing for GuildChannel!
Well of course. A guild channel includes:
A. TextChannels
B. Voice Channels
C. Category Channels
You want to look at TextChannels, which extend GuildChannels
I noticed that a lot of properties are missing in https://discord.js.org/#/docs/main/11.3.2/class/TextChannel (which is the stable version) comparing to the master version of docs
The master branch is the in-development version of v12.