I'd like to think it's not necessarily a tactical issue. Spalletti uses virtually the same variation of a 4-3-3, with some differences, as he used at Roma. He doesn't use the formation without tweaks to instruction. I've really only noticed changes in the way they play in defense, but it doesn't seem like a leaky defense is really the issue either. They've let in just around the same as 3rd place Roma.
I think a major issue is a lack of confidence, increasing complacency and a lack of risk (no tienen huevos). Another issue is probably a thin squad. Eder is not a good back-up for a class player like Icardi, and Inter's stubbornness to integrate youth (they seem happier to list their loan status) seems like a death nail. If Inter doesn't have enough confidence in their youth academy, I'd suggest they use some of that money they make off of loans and transfers to probably attempt to work on that. Inter's ability to sign class players is almost as bad as their ability to spot a good youth player and actually have them integrated, fully, into their 1st team. That is a broken system, and needs fixing. Whether it be an emphasis on youth development or increased success in the market. It needs to be fixed.
Still, I think a core issue is a complacent squad. Besides a few players, there is no consistently strong player in most positions. They don't get benched, reprimanded or even criticized, from the looks of it. I've seen many people suggest that they begin to scrap away their older squad members and rotate in hungrier youngsters I have to agree, but I have to say that they need senior squad members. Anywho, I think a culture change if not a total re-doing of the squad is necessary. The current state of affairs in the Inter locker room just seems like a prissy primadonna ridden hell hole, from afar. I may be wrong, but as a spectator, that seems to be the biggest issue.
As for the squad following direction, I think it's evident. Inter's play is actually pretty structured if you subtract the underperforming fuckheads and the careless mistakes. But that brings me to the point that there's no benefit in following direction when those that follow it, can give less of a shit. The players barring a few, don't seem to care. The ones that do care seem like the ones most likely to leave, and hell even the loan signings have more passion in their legs and they aren't gonna be there for another 8 months. lol. Somethings wrong, and the poor on-pitch exploits are only a side effect.
I don't wanna blame the squad members, solely, but they sure do embody the mismanagement, carelessness, and emptiness that the board and higher-ups seem to partake in. Serious work needs to be to clean up the oil leak that has contaminated the entire club. It starts with clueless owners, half-ass board, and passionless players. i can't really blame Spalletti, because he's done a lot better with a lot less. He may lack the influence needed to push to make the club into his own vision like the likes of Simeone in Atletico or Heynckes in Bayern, but his tactical awareness seems to be one of the lesser problems.
These are, of course, my views. I may be wrong, may not be.