I have the same problem, on iPhone.
Seems the API URL from the iOS apps are incorrect. Reviewing the tomcat access_log, I see this entry:
"GET /alfresco/service/api/node/1a0b110f-1e09-4ca2-b367-fe25e4964a4e/comments?pageSize=25&startIndex=0&reverse=true HTTP/1.1" 404
But the correct URL should be:
/alfresco/service/api/<strong>comment</strong>/node/<strong>store</strong>/1a0b110f-1e09-4ca2-b367-fe25e4964a4e/comments?pageSize=25&startIndex=0&reverse=true
I have verified that URL correctly displays a JSON response.
iOS app URL is missing both ../comment/.. and ../store/..
Note, these other 404 entries in the access_log exist along with the one for comments:
/alfresco/service/api/node/1a0b110f-1e09-4ca2-b367-fe25e4964a4e/content/thumbnails/doclib?c=queue HTTP/1.1" 404
/alfresco/service/api/node/1a0b110f-1e09-4ca2-b367-fe25e4964a4e/ratings HTTP/1.1" 404
/alfresco/service/api/node/1a0b110f-1e09-4ca2-b367-fe25e4964a4e/tags HTTP/1.1" 404