Data point: I called JAL today, and the agent was able to reserve seats for me. I had requested 17A/C, but I suspect those are blocked for possible bassinet use. I had also asked for 18A/C, as an alternative to 17A/C, but ended up with 18H/K. My flight is next year, and I know that sometimes seating gets moved around, but I am happy to have the current seats assigned. Still no idea why it kept giving me an error code online. I had tried Chrome as well as Safari to see if it was a browser issue. Anyway, seats are reserved, which is what i had wanted to get done.