Imaze Rhiano It's your avatar's bounding box which is attached to the vehicle when sitting on it. In some cases on a failing sim crossing you get disconnected from SL but your bounding box stays linked to the vehicle. That is the gray box.

Maestro Linden I have been observing this bug for several years but it is quite rare and I have no idea what exactly can trigger it. Driving through region corners seems to increase its chance, though. Definitely not something that can be reproduced directly.

I've seen that happening for years but much more often recently, Maestro Linden, look at the screenshot, having an child prim owned by a different owner than root prim is technically not possible but it happens.

In some cases, a box is created to replace a lost avatar, it is created and woned by the missing avatar, linked to the vehicle at the same position the avatar was sitting and it's size is the avatar bounding box.

if the vehicle is modifiable, it can be unlinked and will still be owned by the missing avatar (which may not be the owner of the vehicle)

but as said in other comments, I can't see any way to surely reproduce the issue, it's just happening in some special conditions that i've never been able to define

I couldn't find reliable way to reproduce bug.

Somethings to consider - there was 3 avatars sitting on vehicle when failed crossing happened, vehicle was fast moving ship and it is possible that those regions where we were crossing were rarely visited and very empty water regions.

But generally I think that this bug is too hard to reproduce now. It was just weird to see 2 gray boxes that did have different owners to linked ship that did have 3rd owner. Never seen that happening before.

Sorry - I don't have more information to reproduce this bug.

I'm not able to reproduce this with Second Life Release 7.2.2.18475198968 on server 2025-09-16.17777995432. I had 2 avatars sit on a vehicle, with the 2nd avatar wearing many scripted attachments to increase their chance of region crossing failure, then proceeded to drive around the 'Blake Sea' regions.

After a few failed crossings, the script-heavy avatar's viewer showed that they became stuck at a sim border. The remaining avatar continued to see the stuck avatar on the vehicle for a period of ~30 seconds after the failed crossing, before correctly making the stuck avatar disappear from view on the vehicle. I believe this is the correct/expected behavior when some of the passengers on a vehicle fail to cross; there's a certain grace period before the avatar is considered lost and disappears from others' view.