a partial can only come back if it is saved. and the only way to save a partial is to use it.
this means that if it comes back after a relaunch, that it must be in use somewhere in the document.
if you cannot locate it i’d recommend a divide and conquer approach:
make a copy of you document.
then on the copy, delete half the pages. and relaunch.
if the partial comes back again then you know it was s used in the remaining pages.
if the partial is gone then you know it was in the deleted group.
repeat until you’ve located the page.
it’s a quick test and with 8 repetitions you can locate the culprit page in 250. with more modest sized files you’ll be done even quicker. 15 min. tops. 
if you get all the way down to one page, and the partial still comes back. and that seems to be an error, send me the file and i’ll have a look in the debugger and tell you exactly what’s going on.
isaiah