I'm surprised nobody has yet mentioned "engineer" being used in place of technician, installer or operator.
If my cable TV box isn't working, I don't want the company to send an engineer. If they sent a real engineer, they'd be sitting in front of the box with a JTAG probe attached, probably spending days or weeks identifying the true root cause of whatever memory corruption causes the picture to freeze under very specific circumstances.
What I want instead is for them to send a technician, who can follow a prescribed diagnostic procedure, and who will hopefully know from experience that adding a -6dB attenuator in the signal path has a good chance of making it work reliably. Total time taken, about 20 minutes, and my cable box becomes usable again.
Back in the R&D lab, an engineer can (and should) replicate that empirical 'fix', determine exactly how and why it makes the symptoms of some underlying problem better, then fix the code and ensure the fix is rolled into to the next firmware update.
Very different skills, very different job functions, and neither could do the job of the other - yet still the confusion over the title.