MySQL Unique Key Limit
Somehow this was a VIEW that turned into a TABLE?

I checked; the max of 16 columns per index has existed for a 'long time' and applies to 'all' engines.  Reference. I can't explain your specific question.

Also, I am thinking there are worse problems than the failing UNIQUE.

It is unreasonable to normalize something like "location", while also including all the fields in this table:

location_id,city_id,region_id,dma_id,country_id,continent_id

That is, there should be a different table with all of those columns, but only location_id in this table.

I recommend you manually remove the UNIQUE line, load the data, then clean up messes such as location_id.