I experience the same problem, it has screwed me over twice now during training/ftx's.
I'm not a computer guy, but all the research
i've done shows the following.
It's a memory issue that has something to do with ArmA3 reaching maximum memory due to the extremities that Tanoa entails. For whatever reason, ArmA3 fails to ask the CPU for extra allotted memory to compensate.
The issue has persisted for a year now, Bi is aware of it and has failed to produce a fix.
I have no clue why it only happens to a select few people. My computer is on the lower end in terms of capability but I do not believe that has to do with the glitch occurring.
At present there appears to be no fix.
For my most recent training I have lowered my view distance to 1000 and object distance to 500 and it was completely fine until things REALLY hit the fan at the very end, then the issue persisted.
Wish I knew a fix but so far the interweb has nothing. thinking about buying a new computer myself personally but even then, who knows if that will correct it.