I can reproduce this issue. Has anyone else seen this? I'm using TestStand 2019 r2.
1. Create custom rules and add multiple Analysis Modules in the respective tab.
2. Click Export and check all the items. At this point you should also have multiple items at the bottom under the Analysis Modules section.
3. Click Export and you will get a prompt to select a file to save rules to.
4. Delete all your current available rules and import the file you just created. You should notice you have only 1 Analysis module instead of the multiples you checked.
The problem appears to be when exporting in step 3 above as it will only save the last Analysis Module checked. I verified by adding another and exporting again where it was now the only one saved.
This is a big issue when trying to import between developers.