The thread is 8-40.
Can you tell if there is a gap between the receiver and the forearm? Something seems to be putting abnormal pressure on that screw.
With the forend installed, screw tight, I can feel and see no more than a business card or less of a gap at one point of the rear of the forend stock. But elsewhere around the forend it is snug to the receiver.
Placing that business card in that same spot with the forend screw out, then feeling forend as I remove the business card, it does seem to move further into the receiver just a tiny bit.
I had previously thought about putting a spacer inside between the inner diameter of the receiver and the forend tenon that fits in there. But, my lack of experience told me don’t go guessing.
Not totally sure, but under recoil something must be moving enough to loosen a fairly poorly holding screw. Maybe forend is shifting fore/aft if only 1/64”?
