But the problem is.....
FMC coding errors.....a few years back they introduced a new lat long convention which resulted in dozens of aircraft following ( very accurately) the wrong route.
Also seen when manually entered flight plans either (1) Don't spot the half degree or (2) As again happens only too frequently enter the wrong lat/long (normally by one degree).
The another issue is solar storms taking satellites out. We are in a major cycle of solar activity for the next few years ( it is why we have more HF problems than we did a few years back).
The other problem is lack of awareness of tracks flying above them on random routes. Again plenty of TCAS warnings in recent years where aircraft have descended when crossing tracks. Presumably they didn't parallel the tracks because they didn't know where they were.