Using # in custom menu causes 404 when using custom permalinks

So here is the scoop after much troubleshooting. We have a number of Navigation menus. On some of those menus, we want the parent to not be clickable/usable.

In the old days, we chose Custom and then blanked the URL. In later releases this caused our menu to display incorrectly and so we switched to #, which to my understand what we were supposed to do. Several upgrades have gone by and we have now had a user report getting a 404 when clicking on a parent menu. During our troubleshooting process we found where this happened to one person and the issue ended up being custom permalinks. When the individual went back to default permalinks, everything worked fine. There were no comments in the thread and no apparent resolution. In addition, that thread was over a year old.

Here is the custom permalink structure I am using:

/%post_id%/%category%/%postname%/

Is there any fix for this? Any idea what I am doing wrong? This isn’t a complex site by any stretch of the imagination.