A WD hard drive can be detected by one Macbook but not another A WD My Passport hard drive (bought in 2016-7) can be detected by one Macbook (a 2018 15" MacBook Pro) but not another (not even in diskutil) (a 2013 11" Macbook Air). What is the explanation for this? Has it got to do with something along the lines of differences in design in the motherboard (eg. different voltage ranges for logic levels)
The common cause of a bus powered drive not operating is the computer isn’t getting enough power through the cable you are using to power the unit. 


USB external hard drive is mounted on one MacBook Pro but not another
External hard drive not recognised by MacBook Pro.
USB Hard drive has very small chance of being recognized by Macbook Pro each time it is connected, but works with other machines


Swapping cables or using a powered hub or getting a new enclosure can help triage and isolate why this happens in many cases. Also, looking for a long running fsckprocess I’m case the “good” mac is actually triggering an “unclean mount” type check. That often delays a device from mounting, but you should see it in diskutil immediately which doesn’t match your case here.