Tried to edit an activity which has been working fine before. I get an message: ERROR Referring to invalid nodes. Tried removing different audiences one-by-one but cannot save any modifications to the activity. I tried copying the activity which worked but could not save nor modify the copy. Target maintenance did occur while I tried saving the activity so I waited until it was done, cleared cache/cookies tried different browsers and incognito mode and still cannot modify the activity.
Other activities in other workspace are not affected - they work fine.
Any idea how to work around this? I dont want to lose the work that was already done as it was considerable.