I tried to ask someone in squad chat if they had Discord and it kept telling me it was blocked due to secure content? Is this a bug or a "feature"?

You cannot use the Letter @ in the ingame chat, as the game thinks, you are telling mail adresses, wich are secure content in some countries. So you can' write someting like: "@ Fusselbirne: Do you have discord?" Just write: "Fusselbirne, do you have discord?"

The solution for discord is really simple, write: Dis cord. yes, write a space in the word. It works for me all the time.

As for the channel address, its the same thing, if your write "discord.gg/abcde1" it won't work. But it will work if you write "dis cord.gg/adcde1"