Mark, we have some orders (from a certain big retail chain) with 4000+ releases. Epicor support gave us a setting for the local client’s SysConfig file that worked for us in both E10.0 and E10.1. This works for both Sales Order and Customer screens.
NOTE: Use at your own risk, backup your database first, test on a copy of your database, etc and other caveats apply
The performance problem you are having add a Ship-To to a Customer can be addressed by setting a value in the SysConfig file. Under UserSettings in the sysconfig, add a node TreeExpandIndicatorThreshold value=“100”
This will tell the tree control to not loop through checking for children/grandchildren etc. if the parent entity has more than 100 nodes in the tree. This will speed up both initial data retrieval and data refresh after an update.
<TreeExpandIndicatorThreshold value="100" />