If anyone comes across this question. WordPress Codex says the following to 'orderby' => 'meta_value' and the order param:
Note also that the sorting will be alphabetical which is fine for strings (i.e. words), but can be unexpected for numbers (e.g. 1, 3, 34, 4, 56, 6, etc, rather than 1, 3, 4, 6, 34, 56 as you might naturally expect).
You are querying event dates, so the order of the results might be wrong because of this alphabetical sorting.