I thought I'd post this information for anyone else who may be looking for the solution. I could not otherwise find a solution here or online, and wanted to keep this in the ether.
In our 1.7.x elastic we had configured a default text analyzer of "snowball". However, in 2.4.x and 5.0.x, this is not allowed. When we have hundreds of indexes which are created on the fly, without pre-knowledge they are going to be created, this was a problem.
You can see here we've created a template called "default" which will apply to all indexes that are created "*" and default to the snowball analyzer. See the templates guide for more settings.