This still happens when you use to setblock a sign like this and reload :
/setblock ~ ~1 ~ standing_sign 0 replace {Text1:"{\"text\":\"TEST\"}"}
This works but i think the other one should works to :
/setblock ~ ~1 ~ standing_sign 0 replace {Text1:"{\"text\":\"TEST\"}",Text2:"{\"text\":\"\"}",Text3:"{\"text\":\"\"}",Text4:"{\"text\":\"\"}"}
This still happens when you use to setblock a sign like this and reload :
This works but i think the other one should works to :