The LAC (Location Area Code) is a number sent to the home carrier (T-Mobile) as part of the registration message. It represents a geographic cellular region, similar to a Zip Code or Area Code. The home carrier can use this information to either approve or deny roaming within a roaming partner's network. In this way, the home carrier can direct you to roam only on the cheapest available carrier. The only two countries where I really suspect T-Mobile may be using this information is Canada and UK. It would really surprise me if they were using it in CR. They haven't really admitted to doing this, even in the US.
I think what you may be seeing is just general "squirreliness" with CR carriers. ICE is known for being a bit odd. If you have not already done so, at your first opportunity, try to contact T-Mobile's direct international support line at +1-505-998-3793. This call is free from a T-Mobile phone. Do you have any back-up voice calling capability (e.g. Skype-Out, Viber)?
Your issue is why I always recommend that international travelers have backup plans.
