I've ran into this issue intermittently over the last year or so. Now I've figured out why it was intermittent for me.
After reviewing enough similar records on the same table trying to find some discrepency between them; I found that the requests which had a 'child task' created and associated with it, I was able to edit the other related lists simply by double-clicking the field.
The requests on that same table that did not have a created 'child task', I was unable to interact with any of the related tables (Approvers, Task_SLAs).
I can't figure out how these two things are linked.
*Update*
I was checking the list control on the 'child task' related list that gets created on some of the requests, and I found that the "omit if empty" checkbox was selected. Ideally, I didn't want to show the related list tab if there were no 'child tasks' created;
Once I unselected that box and went back to a problematic request that did not contain a 'child task', I was then able to edit all the related lists.
I tested this once more by selecting that same checkbox and then revisiting the same problematic request, and sure enough, I was not able to edit the related lists.
I tested this to see if I set another related lists to "omit if empty", would it reproduce the issue?
Unfortunately, setting a different related list to do this did not reproduce the issue. This seemed to be tied directly to this specific list control settings.
