I replaced the washers on a house's foundation bolts (replacing old round washers with larger square washers).
On 6 of the ~30 bolts, the nut was rusted in place and the shaft was eroded where it sat in the sill plate. Trying to unthread the nut just twisted the bolt until it snapped. All the other nuts unthreaded without much effort (and some Liquid Wrench or WD40).
These 6 damaged bolts were the pairs at 3 of the house's corners. What would cause that? (I've replaced these bolts with UFPs, but am wondering if it's a sign of some other issue that should be fixed.)