This error has been replicated in LabVIEW 2017 SP1 DSC. ERR_MergeErrors has a vulnerability in that it will concatenate the "error string" within the password protected calling VIs without limit to the character count. There are undocumented features within LabVIEW DSC that will populate the "error string" and concatenate it with internal messages even if there are no errors or memory leaks within your host code.
In order to track down the source of the memory leak in ERR_MergeErrors, search the vi.lib for this DSC library function, open the front panel, and execute your code while the front panel is open. You can use "Tools >> Profile >> Performance and Memory" to watch the memory grow under certain use cases of LabVIEW DSC. You can copy and past the value of the "error message" indicator to see the contents and get clues to which internal functions within DSC are failing without producing an error message.
I do not believe this vulnerability has been removed in DSC 2018 but it certainly exists and has been documented in LabVIEW 2017 SP1.
