If it's operating like anything else it means they aren't flying from Nassau to RDU on Saturdays. They fly that route every day of the month in October but Saturdays.
My guess is connections no longer work on Saturdays along with a seasonal shift in flight times/routes.
Take a look at the LOW FARE CALENDAR prior to your October dates and you will notice that there are seasonal routes from Nassau to RDU.
- March you're good
- April you're good (except the last Saturday)
- May you're good
- June starting the 10th it doesn't fly home Monday-Friday and only flies on the weekend
- July is the same exact story as June but it's the entire month it's that way of not flying M-F and only flies on the weekend
- August starts back up a normal schedule starting Tuesday the 6th and is available again 7 days a week (except the last weekend of the month)
- September you're good (except the 1st of the month)
- October they stop flying on Saturdays but fly the rest of the week
It's seasonal route adjustments along with connection time adjustments. Flying to a place doesn't have any bearing on flying back to your home destination.
Now November 2nd is a Saturday and presently November 2nd is the last day you can book right now. When the next release opens up and you can see more months I would check again to see if Saturdays, well actually if any one specific day of the week, is Unavailable in November and beyond and I'm going to guess it's because they can't make the connections work and/or they switched into a new seasonal flight time/route.
Your short answer if you're still wanting to book with SWA for your trip is to come home on a different day of the week other than Saturday.
BTW this isn't a SWA only issue. We've experienced it elsewhere too.
ETA: Your trip isn't until 2020 BUT I would expect seasonal routes/connection differences to continue unless SWA announces otherwise for your desired destination and home airport. Just
when those seasonal routes/connection differences fall (as in the days of the week and months they exist) can change.