We are using SparkFun redboards with Chromebooks, currently Chrome v.94 and using the most recent Arduino Create for Education (1.0.17)
After a few sucessful loads students begin to see "Sending 3020: receiveData timeout after 400ms." Having seen similar issues wiht other Chrome-based Arduino IDEs I knew one "solution" is to load a sketch with the WIndows IDE, which seems to "unlock" the Serial port for communication and the Chromebook can the load a few more times before timing out again. Frustrating for students, but it works.
I just discovered a a better "self=help" alternative for my studentrs: If they simply open the Serial Monitor and Disconnect that will free up the Serial port for subsequent loads. Voila! I hope this helps others avoid the frustration we have experienced with the timeout errors.