That would be one way: https://ufile.io/
No item prevents a event from appearing but tehre are two other factors:
-Four Leaf Clover event only spawns in the Underground Gardens.
-Each event only can spawn once per Layer. 1 time in Catacombs, Gardens and Magma Caverns. So that event ususally only can spawn once per run in the Gardens.
1. There was a bug with the Lizard TF item that caused a softlock loop with too many Lizard parts to not choose any option. So that may be the cause? You're talking about Cursed Artefact Spots or what are you refering to with cursed spots?
2. The game setting definitely say the max is 15. I will test it out myself to check.
3. I looked at it but could spot no unusual thing. I will also try it out myself and report back if I spot anything unusual.
Got it!