It's generated from something like : (so using non default rules and custom vias. When I use default rules / tech vias it works just fine)

- analog_io[10] ( PIN analog_io[10] ) ( top_I.branch\[7\].check_mask.block\[15\].um_I.block_7_15.tt_asw_0_I bus ) ( top_I.branch\[15\].check_mask.block\[12\].um_I.block_15_12.tt_asw_0_I bus ) + USE SIGNAL + NONDEFAULTRULE analog_track
      + FIXED met3 ( 2722310 3096710 ) ( 3081640 * ) ( * 3222510 ) ( 3167480 * )
      NEW met4 ( 2723660 3113560 ) ( * 3110860 ) ( 2725010 * ) ( * 3096710 ) analog_via
      NEW met4 ( 2897540 3077160 ) ( * 3079860 ) ( 2896190 * ) ( * 3096710 ) analog_via ;

I am not sure about how the parsing of NONDEFAULTRULE works when it occurs before all of the routes. The way I have been doing it is like this:

- analog_io[10] ( PIN analog_io[10] ) ( top_I.branch\[7\].check_mask.block\[15\].um_I.block_7_15.tt_asw_0_I bus ) ( top_I.branch\[15\].check_mask.block\[12\].um_I.block_15_12.tt_asw_0_I bus ) + USE SIGNAL
      + FIXED met3 TAPERRULE analog_track ( 2722310 3096710 ) ( 3081640 * ) ( * 3222510 ) ( 3167480 * )
      NEW met4 TAPERRULE analog_track ( 2723660 3113560 ) ( * 3110860 ) ( 2725010 * ) ( * 3096710 ) analog_via
      NEW met4 TAPERRULE analog_track ( 2897540 3077160 ) ( * 3079860 ) ( 2896190 * ) ( * 3096710 ) analog_via ;

I will take a look at what the parser is doing.

Just tried like that but same issue.

Great, that cuts down the possibilities.