Luckily it's not game breaking, but annoying nonetheless. After Atila tells me to wait 2 months while he searches for Salvatore, it was optional in the stock game to return to Isabella's house in San Juan and be met with hired goons there. In Maelstrom GoF 2.5 however, they don't spawn at all and I cannot exit the house after entering it.

I don't normally support GOF 2 or GOF 2.5, because I have found they are incomplete projects after the original group abandoned them.  There have been cases of missing or misnamed models, and other problems because I think those two mods were a work in progress...but never completed.  But, people seem to want to play them, so I provide them as they existed.  I think GOF 1.2 is more trouble free and since much of ERAS was based on 1.2, as problems were fixed in ERAS, the corresponding code was also fixed in GOF 1.2, if applicable, because they started from the same place and was easy enough to fix at the same time.

Anyway, my first guess is that character models for that scene are either missing or misnamed, as I mentioned is a common GOF 2/2.5 problem.  If you have a save file from in front of the house, I can enter and if the problem is that simple, I can either fix the model names in the script, or replace missing models from GOF 1.2 for that scene.  If it is a more complex problem than that, I can't guarantee I will devote much time to fixing it in the GOF 2.5 mod, unless of course the problem is due to Maelstrom itself, which I will certainly fix.