It is a bug which happened to me twice over the last 2 days:

-2 or 3 Slugga boyz squad, upgraded with Nob leaders (no burna), and loaded in the same trukk.
-Maps: Angel Gate (3v3) the first time it happened, and the Green tooth Jungle (1v1 ranked) the second time.

The bug:
In both situations I decided to attack some ennemy troops entrenched behind cover close to a wall, a bunker, or the limit of the map, with my Slugga loaded in the trukk. I bring my Trukk next to my target (very close to the targets and the border of the map, or the limits of the pathable ground), and use "Unload all". There comes the bug: one of the Nob leader (a nob leader in both situations) has been dropped in a place he can't reach by foot (maybe because of the unit collision size, since there was a lot of slugga and too few space to unload them).
On angel's gate: it happened in the middle alley, on the right, near one of the 2 bunkers which protect the right victory point. One of those 2 bunker is on an upper hill, but between the bunker and lower hill, there's a small space that units can't reach by foot. I unloaded the trukk in the lower ground, and the nob ended in this space, and got stucked.
On green tooth jungle: near the upper victory point, there's a cover which is near the map's limit. Behind this cover, there's a tiny space between 2 undestructible bush, this space being unreachable by foot. I unloaded the trukk behind the cover, and a nob got stucked in this tiny space.
In both cases, the Nob couldn't move from this location. No path could be made by destroying the ground. I used the weirdboy ability to "push" allied units, but the Nob remains stucked. Retreat doesn't work at all (the "retreat" effect is canceled few seconds after activation). And i couldn't load the squad in the trukk.

Consequences: squad lost. The squad couldn't even capture the victory point which was reachable by the remaining boyz of the mob. The squad couldn't fight in melee.

I got several screenshots for the spot in green tooth jungle, but i never posted there and i can't find out how to upload those screenshots. I also got the replay, but i think the screenshots show what is happening pretty well. I got everything up to date (lowered graphics settings not to slow down online games). While writing this I tried the figure out how to post screenshots there, but at that time I only have the "502 bad gateway" and i can't check the corresponding thread. I'll try to upload them later.

Hope this bug will be explained or even fixed !