When attempting to load attachments larger than 1Mb fail to be uploaded, no error messages are captured in the log files. Fiddler will show an error similar to:
HTTP/1.1 413 Request Entity Too Large
Server: nginx/1.14.0
Date: Tue, 31 Jul 2018 13:52:33 GMT
Content-Type: text/html
Content-Length: 199
Connection: close
Service Desk 14.1 or higher
Internet Information Services
LoadBalancers (nginx or others)
The load balancer that is referenced in the Fiddler trace "Server: nginx/1.14.0" had configured the client_max_body_size to 1Mb causing that higher values wont be able to pass through it.
The error "HTTP/1.1 413 Request Entity Too Large" is a generic error and it wont specify which server caused the error using Fiddler or other proxy tools can help to find out the root cause.
In the load balancer configuration, update the value for the setting client_max_body_size which may have a default setting to 1Mb and increase as needed