I've been bothered by the crayon smell in my 2014 428i, and recently found the root cause:
the upper sound insulating dash panel(part number: 51487221965)
it's breaking down, and that's the source of crayon smell
it's difficult to discover the cause, due to the location: inside the dashboard
pry off the dashboard cover(51459239303), then you can find the strong crayon smell
please check this information on youtube
BMW must be responsible for this issue instead of masking it with other scent.
Perhaps the government should investigate this issue for the bad smell may distract the driver's attention.