Still experiencing this problem in various projects. Whenever a parameter is changed (specifically the length of the line and/or the Custom Marker Name), the grid line disappears from one or more stories, and the story settings cannot be restored. Cannot tell if this is Teamwork-related, as almost all projects within our office are now Teamworked, but here is my work-around:
Create a new file -- make sure the new file has same number of stories as the original. Trace the Grid Objects with lines in the original file and cut/paste into the new file. Create new Grid Objects with the desired settings (for instance, Show on Selected Stories...) and then cut/paste these into the original file. Seems silly, but it works.
MacBook Pro Apple M2 Max, 96 GB of RAM
AC27 US (5003) on Mac OS Ventura 13.6.2
Started on AC4.0 in 91/92/93; full-time user since AC8.1 in 2004