The is a typo in the error message for the /gamemode command. The message says "gqmemode" instead of gamemode. Here, I used a generic phrase "lol", to prompt the error message, though anything will work.
MCPE-35554
/gamemode Error Message typo
Resolved
Cannot Reproduce
0
I was unable to reproduce this typo. Did you try the command again but with the proper spelling of 'gamemode' ? You might have misspelled 'gamemode' since you are using a phone (probably with qwerty keypad)