I frequently use a Rename setting of Custom Text_Original number suffix, used to add descriptors in filenames.
This just started: the Rename action will get the first few renamed files correct (leaving _nnnn portion unchanged) -- but for the rest of the batch, _Original number suffix is stripped and changed according to default duplicate-file-handler routine: _-1, _-2 . . . ad nauseam. My original numbers are destroyed, no undo possible.
Original numbers are created in a batch. There is nothing odd about them to choke the rename code.
What up? Been using LR since V1. This is new. Very time-consuming to haggle with.