After tuning in to the English speaking casters at DH Masters my ears are hurting too much. The "jam" in Jamppi is not the same as in "jumpy", but more like in "yummy" (maybe someone can come up with a better example). You can hear many instances of the correct pronunciation in e.g. this or this clip.
EDIT: And I noticed the casters already changed how they say it. Thank you, much love <3
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