Hello. I have been working with Revit for a few years and have always had this issue. Lets use a lighting fixture schedule as the example. When I place a fixture within the model and want to assign information to it on the schedule that was created, all is fine. As soon as I go and change a parameter for the lighting fixture family or anything of the like, all the information for that specific fixture type disappears within the schedule. Why is this?
I find myself retyping the same information sometimes up to 4-5 times throughout a project when fixture types have changed or quantities have changed and whatnot. This happens with motors, lighting fixtures, special purpose outlets, etc.
Is there anyway to prevent this information from disappearing within my schedules when updating things within my familes?
I've not yet encountered any situation in which information just vanishes. In your Schedules' Properties, is the "Itemize Every Instances" option disabled under the 'Sorting/Grouping' tab? This would be the simplest possible cause - when multiple elements are grouped together in the same line of a Schedule and the have differing values for a field, then that field will appear blank. Perhaps after the data was entered, new elements were placed, thus causing this apparent loss of data (especially if the field is an Instance Parameter). If there is any confusion, can you post an image of the 'Sorting/Grouping' tab of your Schedule's Properties?