EDIT: Well, if silverforce's assessment is correct, it must be a collision issue. Any way of taking your mine/laser collision code out from the main game, to see if you can reproduce the lagging in a simpler context that you could share?
/EDIT
2 secs...that is quite bad. The only times I've seen halting that bad is when I've tried to do something crazy like spawn 1000 objects in a single tick.
Some possibilities:
1. Are you using the Line-Of-Sight behavior on any of your enemies? Silverforce's comment made me think of this, as I tried to use LOS for lasers once. LOS can really grind a game to a halt if it's used incorrectly.
2. Save states, as per Aurel's suggestion, can cause a pretty bad halt if you try to use them during gameplay.
3. You say your demo was exported before the new troubles with node. How far back? I seem to remember than there were janking/halting issues with some previous versions of node as well. 10.5 really seems to be the sweet spot.
Seems like something is definitely amiss here. Hope you can figure it out!