SIGN/COMMAND BLOCK BUG

When I place a sign, or enter a command in a command block, sometimes my hotbar disseapears. The only way to solve this problem is to save and quit, then re-join the world. Sometimes, I have to write a lot of stuff on signs, and having to save and quit each time I finish writing something, is extremely annoying. I am playing on a Huawei Honor 8.