It is possible to take a low obedience and high grade slave and meet with them, gain consent for sex, but the slave is still resisting sex in immediately ensuing sex sequence. Subdue will continue the sex action with mental stat losses. Stopping sex will leave the slave on low obedience with no further interactions possible that day. It's just a bad result for the player with no warning it can happen.
I'm guessing this is due to line 620 in newsexsystem.gd which only checks obedience when determining resistance. I am not at all familiar with the sex coding so I can't offer any solutions.
Any players wanting a workaround for the problem : presumably meet with these slaves once to raise their obedience then meet them again to get sexual consent.