The bedding compound got into the bolt lug recess through the front action screw through-hole because the tip of the screw pushed it up there when you inserted the screw to secure the rifle in the stock for curing.
There's a couple of different ways to avoid those sort of "corner locks", when bedding compound gets around a sharp edge or corner where it shouldn't and locks something up - usually the metal to the stock.
The first is to fill every single area, where the compound can flow or get pushed, with an easily removed filler, like modeling clay or thick paste wax - which is what I pack into all threaded holes, through-holes or not.
Secondly, to avoid pushing the uncured compound with a screw (the screw(s) should be loaded with unbuffed paste wax), either insert the coated screw B 4 applying the bedding compound (hold it in w/tape from below) so the tip threads are above the wet compound; or use a large clamp to hold the barreled action in the stock while the bedding partially cures (the screw hole can be poked/drilled through the thin bedding layer later).
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