Could you please share us with a sample or a screenshot to show more detailed information?
Such as the formula you use, the lookup value and the matched value in return array.
It's recommend to create a new blank worksheet, and copy part of the data to this worksheet to test whether the amount of data affects the results of Xlookup function.
In addintion, you may use other query functions (Such as Vlookup) to replace Xlookup function, check whether this issue could be reproduced.
Please make sure the lookup value and values in the lookup arrary are spelled correctly and do not contain extra space.
The type of lookup value is the same as the type of values in lookup arrary.
Please also ensure the lookup array contains all required values, you may use "$" to make lookup array provided to the formula is correct.
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