I am having a similar issue, I have a quarterly data that the excel and R brings different values e.g. the following in excel =XIRR(I2:I28, B2:B28) brings a value of 2.9802E-09.

In R the following code:
xirr(cf = NCF, d = Date, comp_freq = 4,maxiter=100, tol=0.00000001, lower =0,upper = 10) brings a value of -0.612.

I am not really sure what is driving this discrepancy. Can someone please help?