I have successfully installed MongoDB 3.6.1 on High Sierra. It starts up correctly and the mongo command runs.
When I send a POST request (from Postman) to my REST service, it stores a new document but only with the document id - no data items from my schema have their data stored. When I try and insert data using the Mongo shell, that also does not store the data.
I have also tried this on Sierra using MongoDB 3.0.7 (I didnt upgrade this after seeing the above) and the results using the REST API and the direct Mongo shell insert give the same results - i.e. no data is stored.
Can anyone advise how to get MongoDB working on Sierra / High Sierra yet? There have been reported issues re using APFS (High Sierra) but Sierra also fails as described.