I've noticed similar behavior in my 2010 Insight LX. When I lock/unlock the doors, only one of the two license plate lights flashes. I thought a bulb was burned out, so I bought replacements. But when I turned on the low-beam lights, I saw that both license plate lights were on. Curious...
2010 Honda Insight LX, CVT, Silver (2019-), 177k miles at purchase
1995 Honda Accord LX, 5-speed manual, Gold (2000-2019), 313k miles (retired)
1986 Honda Accord LX, 5-speed manual, Gold (1992-2000), 173k miles (R.I.P.)