OK, then what are you doing in code that is overriding the montage?
Has to be something specific like triggering a different montage, or causing all montages to stop.
If you removed everything except the slot node, you have no underlying animations at all, so there’s nothing appening at the animation level except for montages.
Meaning the issue cannot be code rotating or moving the character or any gameplay thing that doesn’t spwcifically deal with montages.
Not necessarily related to the same slot though if its a rogue stop montage node.