This has happened to me twice now, I think both times with Goliath. I am unable to purchase merc training from compound when I am at full supply. I cancel the unit that is training because I thought that might be the problem, but the upgrade is actually grayed out as if it is a unit that still needs an upgrade in order to get merc training (sniper, lancer, etc.).

It's entirely possible that I'm just missing something. I'll try to find the replays. It doesn't seem like it makes sense for a full supply to stop you from buying merc training does it?

Post replay or screen shots if you can. I don't know if upgrades count as supply. If they do, it would make sense why you can not purchase them at full supply.

As for multi-lock, I believe the attack information on their goliath's command card 'greys out' as they are attacking something in the air.