The MAX10 board uses analog switches to connect the JTAG pins of the MAX 10 device to the JTAG header or EFM32 microcontroller on the Sensor board.

By connecting the USB Blaster to the JTAG header, pin 2 of the JTAG header is connected to GND, which causes the analog switch to connect the JTAG pin to the JTAG header and disconnect it to the EFM32.
As a result, even if a personality using FPGA is selected, the EFM32 microcomputer cannot program the FPGA and loading the personality fails.

Be sure to pull out the USB Blaster first to load Personality.
If you want to rewrite your FPGA design via the JTAG header, do so after the Personality is loaded.