I have this issue as well (Xbox One, Realms, 1.17.40). Whenever I apply dye or squid ink to the sign, it makes a little squelching sound and the text disappears.
I have this issue as well (Xbox One, Realms, 1.17.40). Whenever I apply dye or squid ink to the sign, it makes a little squelching sound and the text disappears.