I wonder if an earlier bolt was swapped in? I've noticed that very earlier bolts (pre-Hi-Speed) had a slightly shorter locking lug and took a slightly longer locking end on the lever. I wonder how many slightly different bolts have been used - I have a newer Hi-Speed bolt & lever that will not work together, the slot in the bolt is not wide enough for the locking end of the lever which is noticeably thicker when compared to an early lever. I put the late lever in an old 1891 that locks up tight with the original lever and there is a gap left between the locking surfaces which allows the bolt to move back & forth slightly with the lever closed.
There are some comparison pictures of early & late bolts here -
.rimfirecentral.com/showpost.=11628557
