Sorry I didn't answer your question since I thought it was obvious what I thought. Yes, if that hub had a problem, I would be suspecting all 3 to have a similar potential issue.I asked you a question and you skated around it. Why?
It's a double axle trailer. All four have drum brakes, all 4 get the similar heat, see similar distance, all 4 are the same age. If one blows due to "no maintenance" then how come the other 3 didn't?
So what did you do? Just spin the other 3 and call it your preventative maintenance? My guess is you had to replace the entire axle since you like wiped out the spindle on that side.