D8 Views - Contextual Filter by Month & Year? (Content date field)
Remove your date contextual filter, by clicking remove.
click Add a contextual filter, and search for the date field and select the "Year+month" granularity. Then click add. 




once you are done you should have your contextual filter look like this:



Now you can go events/201807 and it would give you the same results.

update: this granularity is available for all date fields under the contextual filter option (node.field_somedatefield (year_month) provided the field has been added normally using content types manage fields section: