Actually, this explanation doesn't match my observations. I get this issue even in soloplay and years before 1.69 that brought "space" for player characters. Also no placeable is needed to be around.
From what I observed, it happens only in multiplayer and only in very specific areas. Usually one or two areas on whole PW (if is small or medium). So the solution could be to rework them or do minor modifications in tiles till it stops.
On the PW I mentioned, one of the areas that was notorious for glitched transitioning was only 8 x 8 and utilised the Bioware City Exterior tileset. Folks will often find themselves trapped on a wall that had no path down when transitioning into a transition almost directly opposite of it on the same map. Even before the PW adopted the CEP, this had been an issue. Twice the map was remade (same tileset) and the glitch remained. Later, after CEP 2.2 was added, the map was further modified using the tileset extension option (we added alleys there and a ramp was placed on that wall so folks wouldn't need a DM to port them down if stuck anymore. Folks however still often ended up there. We took notes and found out it never happened if just one PC/Creature transitioned. Groups and PCs with followers were the ones getting stuck.
Other maps, during resizing/splitting them, the problems all but disappeared. During this same time period, other steps we being taken to decrease the constant CPU load and reduce lag in general. As lag decreased, transitioning glitches did as well. Areas still prone to the glitch were those usually not yet split or shrunk. Players also played a big part. Those in groups would often -take turns- transitioning and after transitioning take a step forward or to the side to make room for the next to follow. Familiars/Companions and summons were also barred from being used in towns and casters rarely got stuck after that. Over the next few years, as areas were optimized and shrunk or split, lag decreased even more and the problem simply disappeared. While large areas were always the most prone to glitches, a few small ones commonly did as well. Reducing lag seemed to have the most pronounced effect on transitioning glitches, though reducing the shear size of many maps calculates into decreasing lag too. As for -size- not mattering, when this same server updated from 1.68 to 1.69, the number of folks having transitioning issues dramatically increased overnight.
During and since that time, I've had the occasional glitch on my own PW. Once again, the culprit was usually a map that was too large or transition zones that contained too many path blocking placeables near/in them. One thing I did was to nolonger set transitions from one to another. I instead set all transitions (even doorways) to a targetted waypoint and made sure to place the waypoints with a bit of breathing room from the transitions/doors. I also have a "No Bumping" feature players can turn on (which shrinks your personal bubble to near zero) and most do. Its now been years since I've heard or witnessed a PC having a transitioning issue, though on rare, very rare occasions and usually in a group, a PC with one or more -followers- will get a follower bumped across a map still and retransitioning will resolve that if desired.