I have created my own channel in which i have imported videos and excercise from khan academy english channel.
i had imported the following
Writing basic expressions with variables
Algebraic expression to verbal statement
For both the excercise , i was not able to see the textbox as shown in snapshot shown below
After i clicked on the place where text box should be there, then only i was able to see the textbox as shown in snapshot given below
browser used firefox 52.6.0 esr, chrome 68.0.3440.75