xtivreg2 gives different standard error than xtivreg (or ivreg) and ivreg2 for panel data

Dear all,

Consider the following codes which uses the same data but uses four different functions:

//1: use xtivreg (with two-way fixed effects)

//2. use xtivreg2 (with two-way fixed effects)

//3: use ivreg (with two-way fixed effects)

//4. use ivreg2 (with two-way fixed effects)
Summary:
ivreg and xtivreg yield the same standard error. However, ivreg2 and xtivreg2 give different standard errors (also different from
standard error of xtivreg (or ivreg)). I would appreciate if someone could highlight the reason for difference.

Thank you.