Judging from the voltage relationship between the phases of your two transformers, the main reason for this situation is that the initial phase angle of the output currents of the two transformers is 60 degrees different, that is, the A of 1 is 60 degrees different from the A of the two circuits, and the B and C phases are also 60 degrees different. You can draw the phasor (vector diagram) of the output voltage of two transformers, and it is easy to see the results you listed. The main reasons for this result are as follows:
1. The connection groups of the two transformers are the same, but the inputs come from different power grids. Because the voltages of the two power grids are not synchronized (that is, the initial phase angles of the voltages are different), the difference is about 60 degrees.
2. The connection groups of the two transformers are different, and the input comes from one power grid. In this case, it is mainly caused by different connection groups of two transformers.