As titled 
Since collection output is not supported in the text exporter / copy paster templates, I wanted to use memex tags to export to [[tag]] but I get [[#tag]] instead.
Can you post the template you use here?
On quick response, there are 2 ways of exporting the tags, once with and one without the #
See for “as string” or “as iterable object” https://worldbrain.io/tutorials/text-exporter