Abbreviation: ME = MultiExcerpt
The symptom of this problem is that ME-Include does not work across spaces. It cannot find the ME that is in another space. The broken page has been copied or moved from its original location.
In this case there is no "SpaceWithExcerpt" parameter in the ME-Include macro, only a "PageWithExcerpt" parameter (visible by viewing the Storage Format markup of the page). In an old version of the ME plugin there were problems with ME Includes across spaces. That problem was fixed in a way that broke some old ME-Includes that did not have a "SpaceWithExcerpt" parameter: when those ME-Includes are on pages that are copied or moved their “PageWithExcerpt” parameter gets damaged.
The broken ME-Includes only had a "PageWithExcerpt" parameter before they were copied/moved and it was for an include of an ME in another space. That "PageWithExcerpt" parameter had the key of the other space prepended to the page name like "TS:My Test Page". After a move or copy the “PageWithExcerpt” parameter may be corrupted by prepending the new location’s space key to the original value like “TS2:TS:My Test Page”, breaking the include because there is no page “TS:My Test Page” in the space TS2.
To solve the problem you can do this to the original pages and to any moved/copied pages that are broken: add a “SpaceWithExcerpt” parameter and repair the “PageWithExcerpt” parameter. This can be done automatically by editing the ME-Include macro in the macro editor:
open the page in edit mode (the page with the ME-Include that includes an ME from another space)
open the ME-Include in edit mode
populate the "Space With Excerpt" input with the space that the ME lives in
verify that the "Page With Excerpt" is just a page name, not a space key prepended with ":" to a page name
save the macro, publish the page
The goal of the workaround is to populate <ac:parameter ac:name="SpaceWithExcerpt"> for the macro (visible by viewing the Storage Format of the page)
CMEP-251 MultiExcerpt Include - Server across spaces not working after copy/move