There is always a "special" IO site driving a pin with the PUDC_B special function. Vivado always configures the site as an input regardless of whether it is used by the design or not. We don't do that in Symbiflow correctly.

The script fasm2frames.py as an option --emit_pudc_b_pullup which forces emission of fasm features which make the site LVCMOS25 or LVCMOS33 input.

However, when the bank uses a different IOSTANDARD (such as eg. LVCMOS18) those features need to be changed accordingly to make the site input of the same IOSTANDARD as the whole bank (or at least compatible).