Over the past couple of months I have occasionally been losing my PowerPivot Slicers in Excel when using the PowerPivot 2012 add-in. I have now managed to put together a repro for the issue and will outline this below.
The issue has been reported via Connect, so should receive attention soon. Until that point, this blog post provides my own (unofficial) description of the problem and how to avoid it, in case other people are hitting it.
The workbook will initially work as normal, i.e. slicers appearing and functioning as normal:
At some point later (maybe hours, days or weeks), you will re-open the workbook and the slicers will appear very broken. Sometimes they disappear completely, at other times they change size. They often get dropped from the "Slicers Vertical" and "Slicers Horizontal" sections in the PowerPivot Field List, e.g.
Unfortunately the issue is present in both the RTM and CU2 releases of the add-in. (I have only tested the RTM x86 and CU2 x86 add-ins so cannot definitely say if the issue is present in other releases).
The clue to avoiding the issue is in step 2 above...i.e.
Ensure the PowerPivot Model is loaded into Excel before opening the PowerPivot window to refresh. Or put even more simply...
ALWAYS CLICK ON A PIVOTTABLE, PIVOTCHART OR
SLICER BEFORE OPENING THE POWERPIVOT WINDOW
And, with that, you should be able to continue to use your Slicers.
More details (and probably future updates to this issue) will be found on Connect:
The Connect item also includes example files plus a short video to repro the issue.