See here: https://community.powerbi.com/t5/Desktop/Maintain-layer-order-does-not-work-when-published-to-servic...
In neither reports with previously working 'maintain layer order' or new reports this feature seems to be working as expected. I can confirm this was working a week ago, but no longer does.
Can be reproduced by the following steps:
1. Create a new .pbix file
2. Create a rectangle in one color (blue)
3. Create a second object (can be anything - slicer, button, shape all tested) in a different color (red)
4. Send the first rectangle to back in case it isn't already (it should already be in back)
5. Select blue rectangle, tick 'Maintain Layer Order'
6. Upload to service
7. Click blue rectangle
Observed results: Blue rectangle covers up the red rectangle and layer order is not maintained
Expected results: When clicking the blue rectangle, layer order should be maintained and it should not cover up the red rectangle.