sellitemsmarket offeranonymous checkbox issue

PROBLEM: The function below only sometimes clicks the anonymous checkbox.
sellitemsmarket ( string itemname, number price , number amount , optional bool createoffer , optional bool offeranonymous )

GOAL: To ensure checkbox for anonymous offer is ticked 100% of the time.

POSSIBLE CAUSE: Function executes too quickly, skipping part of the method. (Like skipping "hi" to npc and saying "trade" right away.)

I've tried 2 variations of the above fuction::

Code:

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sellitemsmarket("Demon Shield", 29900, 1, true, true)  --> creates the offer, sometimes checks the anonymous offer box.

sellitemsmarket("Demon Shield", 29900, 1, true) --> creates the offer, sometimes checks anonymous offer box. (By default supposed to create anonymous offer)

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Adding wait times before/after the function doesn't change the outcome.
So I tried playing with mouse settings, the click time, which seems to make a difference but I'm unsure. Tried 250-400, 150-250, 1000-1050(this last one stalls the market operation altogether)

Is there a way to get into the bot code itself and re-code the function to give more time to click the checkbox?
What other approaches could I take to possibly solve this problem?

Thank you for reading, and for the possible suggestions that you may have :D

sellitemsmarket("Demon Shield", 29900, 1, true, true)
What happens 100% of the time in script is:

1.Types Demon Shield in search
1.Selects sell
2.Types in price
3.Types amount
4.Places the offer on the market.

What it misses around 40-70% of the time is the anonymous offer checkbox. When set true for optional bool offeranonymous. And same happens when optional bool offeranonymous is left blank (docs say it defaults to true).