Block placing/breaking not being remembered in nether

farther out in the nether along my highway, when i was mining out a section... when i went back to my base for resources and came back, i found that it only saved my progress to a point. after some testing, i have determined that any block placing or breaking before a point is saved and beyond is deleted. please fix this soon, i need it fixed to complete my highway. i would attach a few versions of the world, but just 1 exceeds the max file size. again, been playing Awhile.