QA-OB-3: My disc hit a flexible fence from the OB side. Was the disc briefly over in-bounds when the fence flexed, or perhaps by having slightly penetrated a hole in the fence?

No. The fence defines an OB plane which flexes as the fence flexes. Unless the disc has penetrated and remained lodged within the fence, the fence is considered to be a continuous impenetrable surface. Your disc was not in-bounds at any point when it struck the fence.