I believe I have finally solved the problem. The logs and their tests revealed that the plugin's workflow was correct; disabling BattleCore solved the problem, so it became clear that both plugins were modifying the same properties of the battle screen.
When comparing the behavior of the two plugins, the problem occurred because BattleCore alters the structure of where the actor sprites are stored on the battle screen (it uses specific containers instead of the standard _battleField of RPG Maker MZ).
In my plugin, the system tries to remove the old sprite by searching for it directly in _battleField. Since BattleCore moved this sprite to another location, the removal command fails silently, the old sprite (the summoner) remains on the screen, and the new sprite (the summon) is drawn over or under it, creating an overlap or visual glitch.
I updated the version by adding a check to clear the sprite from the BattleCore container if it is active, and in the tests I did here it worked correctly.
Could you download the new version and test it again? I'm optimistic that we've solved the problem this time!