The main issues are:
1. Open and save the layout book as an AC10 file before merging it into the building model (PLN, PLP).
2. If you have been using PMKs instead of direct links to the PLN, relink them in PlotMaker before converting them to an AC10 file.
3. Do not rename the project file (PLN) before merging the layouts. This will prevent the drawings from automatically linking to their associated views. You can either Save As after the merge, or archive the AC9 files before starting the conversion (preferred).