Client on 2013 Advanced had a situation the other day where the custom reports on several module menus disappeared, as did 2 menu items for UDTs under UDT Maintenance. They could still launch them from Public Task Menus, however. Coincidentally, the modification date on MNUMOD.txt changed while I was installing the TTU. Luckily, I had a backup of the file, and replaced it and life was good.
Today, I installed PU8 and the IRD. Coincidentally(really?), MNUMOD.txt changed again as I was installing the IRD. Both at the step recorded in the Activity Log as ""System Data Conversion started for the P/L module"". Weird. Ummm, just out of curiosity, wondering why there is a data conversion for the P/L module.