My Excel Formula is not able to understand Dollar ("$") Sign?

Question

I created an Excel File few months ago, See below.

Today wanted a slight adjustment in the formula.

But today if I go into the cell and just press enter it is giving an error at the first dollar sign? (marked in bold below)

If I remove all the dollar signs, the formula works again, but I don't want to as I have to copy paste the formula over a large range.

=LET(s,IF(TRIM(LOWER([@[FTC Conversion]]))="yes",[@[FTC Conversion Date]],[@[Start Date]]),t,IF(ISBLANK([@[Termination Date]]),DATE(2100,12,31),[@[Termination Date]]),
IF(TRIM(LOWER([@[Employee Type]]))<>"permanent","NA",
    IF(TRIM(LOWER([@[Corporate Functions]]))="yes","NA",
        IF(s>T$2,"NA",
            IF(AND(s>=T$1,s<=T$2),IF(t>T$2,T$3&" New Joiner", "NA"),
                IF(t<T$1,"NA",IF(AND(t>=T$1,t<=T$2),T$3&" Exit",T$3&" HC"))
)))))

I have already tried closing all excel sheets and re-starting excel, even re-started the PC as well.

Anyone has seen this before?