Created attachment 373973 [details]
See test case. There is a while loop does the following twice.
1) append an element to the host and assign a slot name. The slot name is different on each run.
2) create a named slot and append it to the shadow root.
3) assert that the element created is assigned to the slot.
4) remove the element
5) remove the slot
The element should be assigned to the slot correctly on both run.
On the second run the element is not assigned to the slot.
Created attachment 373978 [details]
The 2nd named slot is also broken without step 4 and 5.
Created attachment 374018 [details]
Apparently removing and re-inserting the element can wake it up.