Getting error in uploading document

Hi All,

We are getting validation kind of error while uploading document(/design/application and File upload component). Appian was upgraded from 16.2 to 18.3 a month ago.
we are trying to upload files more than 5MB, system is saying File could not be uploaded, please try uploading it again.
The same this is working fine in TEST environment , Appian Tomcat are in same server.

We tried by setting custom.properties config as below and restarted, there is no luck.
resources.appian.ac.collaboration.MAX_UPLOAD_FILE_SIZE=1024000000

Appian and tomcat are in different servers.

Can anyone please advise to fix this issue.

Thanks.