XIAOMI Mi A1 LTE bands - User manual or website is right?
As per GSM Arena Website: These are the bands of Xiaomi Mi A1 Global Version.

2G bands    GSM 850 / 900 / 1800 / 1900 - SIM 1 &amp; SIM 2

3G bands    HSDPA 850 / 900 / 1900 / 2100

4G bands    LTE band 1(2100), 3(1800), 5(850), 7(2600), 8(900), 20(800), 38(2600), 40(2300)

Also, with GSM Arena's Network Coverage section in Argentina says about these bands:

2G capabilities :GSM 850, GSM 1900

3G capabilities : UMTS 850, UMTS 1900

4G capabilities : LTE 700(28), LTE 1700(4), LTE 2100 (4).

LTE 2100 is listed as Network coverage and Mi A1's band