Most often, this usually begins with the south side of your home, and particularly the lower area.
Terra, unfortunately once masonite siding has begun to craze and swell it's the beginning of the end. You can sand & seal with the most impervious of materials and it will continue to disintegrate. You may slow it's death some, but most repairs to this type of siding, even good repairs, will not last more than a year or two.
The problem usually is first noticed around nailheads, butt joints, along the bottom edge, near caulked cuts such as around doors and windows, and any place where the surface may have been compromised.
Your longest term repair is to replace individual boards which have started to fail, but this will be an ongoing process as others follow.
If it's lap siding and you replace individual boards, use a reciprocal saw to cut the nails from behind the upper board you are not replacing. (blade against the face of the bad board, going up & under the lap above) Then carefully remove the nail head so as to not damage the upper lap, pull out the bad lap, and use sidecutters to remove the balance of the nail behind. Prime and paint the new siding before installing, paying close attention to the bottom edge and ends.
If you sand and seal, do so during a dry, warm weather period, as moisture trapped inside the masonite is the cause of the problem.