Do you have a form that takes a long time to open?
This is because when it opens, the ExecuteQuery command is immediately executed, which executes the query on the database. If the query is very slow you will have to wait a long time. To solve the problem you can disable the automatic execution of the Query when starting the form by disabling the “Auto search” property of your datasource (like shown below)
AX / Dynamics 365 For Finance and Operations blog 