For my first two or three kyu grades I would always stuff up the tai sabaki (body movement drills) even though I knew them well and had no problem during training sessions. The nerves would get the better of me and as sensei called a change to the next movement I would either get out of time with everyone else or do the wrong movement. It looks bad when everyone turns to the left and I step forward
Thankfully I got over it by about 4th-3rd kyu.
Dean.