@PRAVEENZNMD
You are better off using
First(Sort(SharePointList, ID, Descending)).ID
By using the above, you can avoid any future Delegation and/or Data-Row limit issues.
There could be a number of reasons why your original formula isn't working as expected.
EDIT
Note, the above formula will throw a delegation warning but you can ignore this because the formula is getting the First record. If you want to not see that delegation warning (but not remove the delegation issue itself) you can use this formula instead:
With(
{
wFirst: Sort(SharePointList, ID, Descending)
},
First(wFirst).ID
)