I am using Turbotax Business 2023. We added a new member to the LLC last year, and when I am trying to add them the two boxes "This is member's first year as a member" and "The member left the company this year" automatically are checked and I cannot uncheck them.
We have confirmed the experience you describe and are looking into a possible fix.
In the meantime, here is a work-around that will give you the result you need without causing any form errors.
You will need to adjust the ending ownership/profit/loss percentages for all partners so that the totals at the bottom of the Sch K-1 Wks are all 100%. If you see a form with a red exclamation mark or a field in red, click the Errors icon above the forms list to open a footer that describes all errors for that form.
Note that checking the box for change of ownership serves to create the Allocation Worksheet and nothing more. You do not need to report a change in ownership on the return, other than the check boxes on each K-1.
For any box on a form, you can right-click on the box and choose About to obtain more information on what to enter. Any box highlighted in yellow will accept direct input. Green numbers were carried over from last year; blue numbers are direct input. Black numbers are calculated and cannot be changed.
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