On this pic you don`t have radar ON, only EOS lock - so, no LA for R27-ER because radar is off and maybe target is out LA range or bad aspect.
Flashing because you select R27-ER and radar is turned OFF. But when target come closer (in range) you can launch that R27-ER without RADAR and NICE thing is that radar will be ON immediately.
Test it... lock target with EOS, try to launch (you will see flashing), hold your LAUNCH/fire button and wait... missile is launched and RADAR is ON :smilewink:
This is DCS - i don`t know how this work in RL.