Is there any reason "when" isn't a sufficient translation here for "lorsque"?
No reason. "When" is also accepted now.
No, it isn't. Even though it should.
Can we use "quand" to replace "lorsque" here?
Yes, you can.
When is not accepted !!!
Why was he's marked wrong. It's the shortened version of ' he is'
"Whenever he's alone, he reads" is accepted. (You wrote "wherever" in your answer, not "whenever".)
Shouldn't 'once he is alone' also be accepted?
is there a literal translation for 'whenever' in french? because here, 'lorsque' seems to corresponds with both 'whenever' and 'when', but those two words are not quite the same
as in 'when' and 'whenever' dont quite function the same way in english