So with all this upgrade work, did you upgrade the crankcase evacuation system? Boosted engines (even factory turbo engines) can pressurize the crankcase from blow-by. It happens, rings aren’t perfect. Add to that, vacuum lines become pressure lines when the engine is on boost… so they pop off if they are not clamped, same for PCV lines. This is what happens when you modify engines, you push the failure point to the next weak link, you fix that next weak link and find the NEXT weak link.
BTW, did you increase the size of the fuel pump? High boost can require more boost than can be supplied resulting in a lean condition that burns a hole in the piston. Did you reprogram the ECU? On a dyno with a wideband O2 sensor in the car? If you didn’t you are playing with fire. If you can’t reprogram the Hyundai ECU, you will need to replace it with one you can, like a Haltech.
First off, @the_same_mountainbik is right, check the turbo. If the turbo seal is blown, you will see oil at the outlet side of the turbo plumbing all the way to the engine. If the evac system is the issue, you will see it from the evac line to the engine… So then either replace the turbo or re-engineer the evac system.