If after casting Summon Corpse nothing happens - lootable corpse still shows on map, no corpse summoned on the Circle of Power -, I just wait for the bag of loot to appear on the Circle of Power right after the lootable corpse decays:
When the bug happens, Summon Corpse can be casted over and over again, several times, but it will only burn reagents. And now that I have learned the lesson, I just cast it once and wait for the bag to appear.
Note that my Circle of Power was on a roof - probably with less than 50% stability - when the bug happened. After I moved the Circle of Power closer to the walls, with over 80% stability, the bug stopped happening (so far).
Of course I do not know what causes the bug, so I can not guarantee that it will not happen again after moving the Circle of Power.
By the way, logging out and in did not make a difference, only the time elapsed for the corpse to decay was what was required.