This bug(s) by the looks of it has two different iterations, one is when you spectate an ally while waiting for respawns and he dies at the exact moment of respawn, (first video), other one happens when, I quote:
In Frontline when you’ve run out of tanks and are in the free camera mode, if you click a platoon mate to watch from their perspective (not sure if it would work with any random player), sometimes when you respawn you will still be watching their play but you can control your tank.
Source: WG EU Support
As you may have noticed, 3 garage slots can be missing after today’s micropatch.
This is just a display bug, and you can still buy the tanks (for example directly from the tech tree).
Development team is currently working on the fix.
Please accept our apologies for the inconvenience.