Idera Repository Database Server Shutting down

Hi,

We have installed ER/Studio Data Architect 16.5.

When our modellers check IN or Check OUT large diagram, the Repository Database Server Shut Down.

There are also several instances when i login to Data Architect , i get the following error message : 

"10:25:50.015 - Start Repository Login process...
10:25:50.031 - LOG IN request sent to Repository. Waiting for reply ...
10:26:00.421 -

Detail(s) :
Receive File Error -
Please make sure the Repository Database Server and the Repository Event and Dispatch Server are running on your server machine.
00:00:10.421 - Total time for the whole process.

and it require to restart "Repository Database Server" to fix the issue. 

Any idea why this is happening? Do i need to change the memory pool space setting? Does momory Any changes i need to cha

There are 4 Idera services (Repository Communication Server, Repository Event and Dispatch Server, Repository Database Server and Team Server) and we use Oracle 12c