The Since Last Run assistant does not handle postponed transactions correctly.  
I would expect that a transaction marked postponed in the dialog would simply reappear in the next execution of the dialog with same scheduled entry date, but it actually appears with seemingly random entry dates, some of which are 0/0/00 or thousands of years in the future.  Then there is way to correct the dates.

The best work-around I have found is to stop between Since Last Run sessions and edit the scheduled transactions with adjusted start date and number of remaining transactions since that count is also incorrect if used.  However, this does not always work, and if a transaction is scheduled but only appears with a date of 0/0/00 available to enter in the Since Last Run dialog, that will crash GnuCash.

Ignored entries seem to be gone in the next instance of the Since Last Run, but they do not respect the date scheduled in the dialog. They do seem to reduce the remaining count as expected.

I tested this by entering a transaction dated a month in the past to enter weekly.  I set them with no reminder or automatic entry and 11 total entries.

Then the Since Last Run dialog scheduled an entry for each week before today's date, which I changed to postponed for dates after the first scheduled date.

Re-running S L R produces corrupted dates and incorrect counts remaining.

This is in release 2.4.13 on a Windows 7 system.