I have opened a bug ticket for the issue of the topic.
If anybody else can confirm replication of the bug, please vote up!
Full text of the bug report:
The Virtual Arsenal, if applied in a Mission from the calling code in a weapons box, will not display some of the Iron Front in ARMA 3 Main Weapons.
The weapons are: the MI Carbine and the MI Garand.
Also, if you approach and make use of the arsenal / ammobox system whilst carrying these weapons in a mission setting, once you have finished adjusting your load out, these weapons, if you were carrying them,
will have been removed from your inventory.
If you load IFA3 and enter the Arsenal in the Game interface, you will see that the M1 Garand and M1 Carbine are missing.
If you manually add these items to an arsenal in a mission, they will not appear.