If you are on a offset, that offset is your active route (and if you look at crosstrack, the FMC shows you how far away from that route you are). So if you are within 21nm of the route, either side of your dashed magenta line, waypoints will sequence, if you are further than 21 miles they will not.
I cannot explain the 200 mile note.
Your idea of an intercept course with a direct to a waypoint to make things sequence if you are further than 21 miles only work partly. That is not going to get the ADS position sent to ATC from the "active wpt" that was showing that you were going to it, but it now actually behind you as you passed abeam it and you are getting further away from it but still "going to it". So use the the offset function.....