I keep getting 2 items dropped into my inventory, and it seems to coincide with you updating your mod. The mod is Ribbonia, and the items are 3x Elevated Ramp and 3x Pneumatic Press. They made a suggestion to change how that works to the author but this could affect other mods as well so I'm presenting it to you as well. I haven't proven this to be a problem with your mod specifically tho, so just "food for thought" at this point.

I checked with them and this was our brief discord chat:

Loftaris — 10:43
is it possible that it's "skill system" mod ... I have noticed that every time he updates his mod I get the same recipes over and over and over
Samario — 10:43
yeah that would do it
since your mod list is changing, even if just because a version update changed
@Powerscooter 🎀 maybe consider stealing eneas's "drop a chest next to the player" code
since that does correctly only go off once

Ribbonia gives out its starter items whenever the mod list changes, which happens every time any mod updates. With my sporadic frequent updates, it's probably easy to assume some sort of connection, I do not think SkillSystem is affecting it as it does not give items and most it's variables are locked away and applied after the fact.

What Samario says seems to be correct, a version update will refresh the mod and trigger the Ribbonia items again. The Author has it right, one time execution is the way to go, OnChange can make for some interesting interactions, rather than OnInitilise and check against a value to confirm it has not happened before.

Thankyou for raising this all the same, it's important to understand and ensure I am not impacting other mods unintentionally.