From memory, port config is started from rising edge of req input.
OB100 is runned only once, yes it is true that it needs to run to end before other cycles are started. But port config won't stop program cycle, CPU would go to watchdog, as port config is several seconds and PLC cycles long, before new config is used.
OB100 can start port config block, but as done and error bits are setted several cycles afterwards OB100 one scan is scanned, they never will update to from instance DB (DB2) to different memory area.
Locate your port config to normal PLC cycle and start it only when new config are needed. Then it will work.