Mine used to say one of three things : 

{
"Notice.1": "Decay is ON! Make sure your TC has enough resources to stop decay!",
"Notice.2": "Type /shared while looking at the cupboard for sharing options.",
"Notice.3": "Type /codelock to set up auto-codelock options!"
}

Now when they are displayed, they have been shortened to : 

Decay is ON! M
Type /shared w
Type /codelock

Any idea?

The gametip tooltips in Rust are truncated (shortened) in the Rust client as of a couple updates ago.

Bugger. Do you know if they have they been truncated to 14 characters?

Could the dev of this plugin possibly change the plugin to use  GUI Announcement type messages then, please?

I don't know what the limit is on the client at the moment, but it'd be up the dev if they want to change to another method.