The only possible explanation is that field new_add does not exist in BOTH search's datasets; double-check your spelling/punctuation of all fields. It looks like it is supposed to exist in the first/outer search's dataset and you are trying to create it for the second dataset but perhaps you are trying to create it for both datasets and in that case, you forgot to do so for the first/outer dataset! Using coalesce should work for either case. Also, Try to avoid join so how about this:
index=beacon BeaconType=userevent type=addonselected OR index=clickstream | stats values(*) AS * by INID TEST | eval Message=max (pageid) | lookup TGIF Message | eval new_add=coalesce(new_add,Message." , ".'Location Number') | chart count by new_add providername
... View more