What is the difference between the saying of the Muhaddithun (Hadith scholars) in judging a Hadith as being defective (Ma‘lul) or as being declared defective by virtue of Irsaal (disconnected narration)?

The 'علل' (defective/illal) Hadith is one in which a defect impairing its authenticity has been discovered, even though it outwardly appears sound. This defect (illah) may be in the text (matn) or the chain of transmission (sanad). A Hadith may be deemed defective due to its being mursal (lacking a Companion in the chain) or for other reasons. The defect often occurs in the isnad (chain of transmission), which is more common, but it can also occur in the matn (text). A defect in the isnad can sometimes invalidate both the isnad and the matn. For more information, one can refer to specialized books on Hadith terminology.