Allvit does not have a sprung B-pivot so housing loop will have little effect unless it is holding it back from hitting the stop on the hanger nor does it have a B-adjust screw. Not only that but the guide pulley is concentric with the A-pivot, so chain length has no effect on it. Since it's a claw hanger, you can't move the wheel axle in the dropout. Basically there's no normal way to adjust the gap. There are several potential issues, but it is hard to tell without being able to actually diagnose it. Check limit screws and check how the chain is engaging with the cogs, pulleys and if it touches the cage.