When the BizTalk360 portal is taking an inordinately long time to load the pages, even when changing environments and running queries you can try the following-
Custom Cache Implementation
To improve the response time for few of the REST calls we have enabled Active Directory Cache. By default, this option will be disabled. If you have complex NT Group setup, Active directory cache can be enabled to improve the performance.
You can access this from BizTalk360 Settings -> System Settings
Once you have enabled the Cache, and if you do any Active Directory User account changes you will need to either disable and re-enable Active Cache option, as the Cache will now be stored for 2 hours for the BizTalk360 website.