It doesn't remove the permission, MacroDroid just keeps asking for it.This issue is really nothing I can solve in MacroDroid I'm afraid. It's typically caused by an over zealous OS deciding to disable accessibility services in an attempt to avoid anything that can cause battery drain. There may be settings you can change on your device to prevent this happening and you should start by looking at dontkillmyapp.com and ensure you have configured everything there that is possible to configure.
This seems to work very well.You could also try this