Cylinder Leak down test
If the swap has 24k on it id be hard pressed to say the head gaskets are wrong. But if just the short block has 24k then yes, id be wondering.
Sadly this issue is common with hybrids. Causes can be many things... like
-Light weight flywheel installed
-Light weight crank pulley and light flywheel combo
-Vacuum leak after the MAF
-Weak main harness ground or injector harness/intake manifold ground is loose or weak
You havent really tried many things.... Seeing its tuned at Yimi, you should take it to them and have it diagnosed there. The so cal region has LOADS of good shops with subaru knowledge. If you cant perform these tasks your self, Id HIGHLY suggest taking it to a reputable shop and stop wasting time with it on youre own.