Scott wrote...
Another possibility is the value corresponding to the one in T28 (in
column D) was accidentally made a Text value at some point.
....

Yet another possibility is that if T28 and A3:A82 were all numeric,
they may appear equal but actually contain slightly different values.
That is, 2.3 and 2.30000000001 would likely appear the same on screen
as cell values, but they won't be equal in the array formula. First
thing to check is whether the formula =COUNTIF(A3:A82,T28) returns a
positive number.