If you disconnect the opener from the door, does the door go up and down easily without requiring a lot of muscle? I am thinking if the carpenter replaced the bottom strip of wood, he probably released the tension on the springs and either rewound them, or if you had side extension springs, retensioned them. If not tensioned properly, the door could be heavy to lift and put a strain on the opener and mounting.
You described the opener mounts as an X-brace. If it is the thin metal stapping that comes with some of the inexpensive openers, I would replace it with the angle iron with the pre-punched holes that you typically see supporting the ends of the horizontal track. Mount a piece on the ceiling joists, along with two vertical drops to support the opener. Then add a third piece to form a triangle on one side between the ceiling piece and a verticle piece. That should solidify the opener mount. Also, make sure the ceiling joist(s) you attach to are properly supported. Some times a couple pieces of 2 x 4 bracing are needed to stiffen up the joist.