If you search on tag "cat" and tag "dog" in a single step, and that those 2 tags have no common photos, then the tag filter becomes empty. So do other filters. That's because #2027 : if there is no resulting photos, then Piwigo can't find tags related to this empty set of photos and no tags are available in the tag filter.
[search, 14RC1] search on 2 unrelated tags breaks the search
This is a GitHub Issue
repo:Piwigo
owner:Piwigo
Title : [search, 14RC1] search on 2 unrelated tags breaks the search
Issue date:

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If you search on tag "cat" and tag "dog" in a single step, and that those 2 tags have no common photos, then the tag filter becomes empty. So do other filters. That's because #2027 : if there is no resulting photos, then Piwigo can't find tags related to this empty set of photos and no tags are available in the tag filter.
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