AP Invoice job related slow screen rendering


I have a client hosted on AWS with the following specs:

EC2 instance, windows 2019 with Remote Desktop Server, 32GB RAM, 8vCPU, SQL Express hosted on a different AWS Relational Database Service server. All patched up and updated to latest service packs.
The client has 20 Sage 300 users on version 2022 PU3

The client reported slow Sage when creating AP invoices, especially invoices that are Job related. On testing, I realised that when a user signs on and creates the first AP Invoice that is job related, the speed of the screens is fine (grid updates quickly to add the new columns). Subsequent invoice creations are slower and as time passes it seems to get slower and slower. In essence, the rendering of the grid (details lines) seems to be the slowest upon hitting the job related check box and then traversing though using the tab key..

Some users, from time to time report Sage as being slow in other screens as well, no matter if the screen is on job related or not.

We monitor server resources (RDS and database) and they are underutilized. Also, internet connection is monitored and there are no capacity problems.

What could be the problem?