I've now acquired the dev version, 1.11.115081, and I CAN reproduce it very easily.

Extra info: it does not happen if the player is a diver. There's a different animation when reaching the appropriate depth.

Another video, also showing the inability to move after going up/down: http://youtu.be/lFgmuGUgsxA

I should add that this is reproducible in the editor; the NATO special weapons ammo box, a rifleman and a walk out to sea does the trick. The SDAR appears ready to fire very briefly, but then is holstered as depth increases, and that's when it gets stuck.

I haven't tried dev so will take the above reporter's word for it that it's resolved.

Curiously, something I did fixed it for one restart, but it's broken again. I've done a bunch of stuff so it's going to take some narrowing down.

I did see this in some of the RPT logs, but again may be related to my changes:

"Initializing Steam Manager
unable to load subscribed content list. list will be updated from steam
unable to load published content list. list will be updated from steam
unable to load cached items meta info. save and update functionality will be broken
Steam Manager initialized."

and also a reduced version:

"Initializing Steam Manager
unable to load published content list. list will be updated from steam
Steam Manager initialized."

Various experiments with 'meta' made no difference - either copying over an older one, or deleting it.

I also tried deleting all the save content and creating a new one, in case something was corrupt. No help - problem persists on restart. At the time of writing, my meta folder is currently empty, although it wasn't in the first tests.

One modification to my workaround: it's not necessary to exit the mission, except perhaps to replace the PBO. As soon as the files are present, the Load option appears.

Happy to test anything you think of.

I have this error now, as described in the first note. The version of ARMA has not changed; a restart of the game loses all saves. It happens consistently.

Edit: a successful workaround is as follows. Upon restart, backup all the save content in e.g. C:\Users\You\Documents\Arma 3\Saved\steam\mission-name.island\, make a new save, exit the mission, copy the backup back into the folder, use the 'resume' function and then load the appropriate save.

Fair enough - I do understand the nature of the relationship with third party content, but hoped this might be picked up as a fundamental.

I'll try and liaise with the developer to at least get some information about the failed state of the AI units.