Hi David,
I’m pretty sure you can combine metadata contraints and event constraints - but you have to make sure that the event params are at the end of the query as processed. You can’t use faceted navigation with events mode though.
I have a vague recollection of raising a bug about how the query is built from CGI parameters, meaning that the meta constraint is lost because of where it ends up in the built query.
Try building the query directly yourself.
Instead of
meta_4=somevalue
query=%25O>20170913<20170918
use
query= 4:somevalue % O>20170913<20170918
cheers,
Peter