Cannot edit vBulletin page template(s)

We have a Client with a site running vBulletin 5.0.4. They have a problem with editing templates, there is something wrong with the front-end page editor, it won't allow assigning the template style (Default) which means you cannot see a post on the conversation page. PLEASE only bid on this project if you have not solved this problem before. You MUST be able to tell me the problem (as we have a good idea what it is, but will not waste time explaining it over and over again!) before I award you the project. You also must be able to start on this project now, not tomorrow or the next day. We have wasted valuable time on many people who could not fix it after telling us they were vBulletin experts and knew the problem. There are several threads online about the same problem, but none of the fixes work in this case, so we need someone who REALLY knows what they are doing and can prove it before I award this project. Thanks.