The root cause is the bucket is marked as single-site ("origin_site" = default):
cat /db_1525916743_1521375071_1_C89A6E4E-B848-4326-8755-1D614DFA4F9A/.bucketManifest
id,path,"raw_size","event_count","host_count","source_count","sourcetype_count","size_on_disk",modtime,"frozen_in_cluster","origin_site","tsidx_minified","journal_size"
"unix~1~C89A6E4E-B848-4326-8755-1D614DFA4F9A","db_1525916743_1521375071_1_C89A6E4E-B848-4326-8755-1D614DFA4F9A",1104884368,5732042,6,21,5,425193472,1545273340,0,default,0,92858030
change default to site1 should resolve the issue
id,path,"raw_size","event_count","host_count","source_count","sourcetype_count","size_on_disk",modtime,"frozen_in_cluster","origin_site","tsidx_minified","journal_size"
"unix~1~C89A6E4E-B848-4326-8755-1D614DFA4F9A","db_1525916743_1521375071_1_C89A6E4E-B848-4326-8755-1D614DFA4F9A",1104884368,5732042,6,21,5,425193472,1545273340,0,site1,0,92858030
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