Sleep training with mixed results

TL;DR Ferber sleep training has worked wonders for naps and overnight, but bedtime is still terrible. Need help!

Hi peeps, I'm sorry for another sleep-related post but I really need some opinions here. I'm a long-time lurker, finally set up an account so I could ask you lovely people for some support. We started Ferber sleep training for our 6 month old baby (naps and nights), we're having very mixed results and I don't know what we should do.

I used to only be able to get DD to nap if she fell asleep in my arms, either nursing or being rocked, or if we were in the car. Now I can put her down in her cot in her own room and she will roll over and go straight to sleep with no fuss. She only sleeps for about 30 mins each time but I'm not too worried about that just now as I figure she'll stretch the naps out if/when she feels the need.

Through the night she is now excellent. We used to co-sleep and she would wake up at least 3 times through the night and want nursed back to sleep, and now she will only waken once, anytime between 2am and 5.30am and I will feed her and she goes straight back down in her cot, again with no fuss. She then sleeps until around 7.30, if she's still asleep then I will waken her so that it doesn't throw out the nap schedule for the day.

So far, so good! However..... bedtime is still an absolute nightmare and we can't figure out why. We have a routine and have been sticking to it every night, putting her down for the night between 7.30 and 8pm. We are now on night 12 and she has been crying for almost an hour so far. We have had 2 nights out of the 12 when she settled within 30 mins but every other night it's been at least 40 mins. Sometimes she settles quickly, sleeps for half an hour then wakes up and cries for 40 mins or so. This makes me think she is treating bedtime like a nap and wants picked up after the quick snooze. We have tried moving bedtime earlier to 7pm to see if that helps but I think it actually made it worse. We always stick to the time checks in the book and only stay with her for 90 seconds at each check.

Am I missing something? Has anyone else been in this situation? I really, really want to go and cuddle my baby but I'm also so reluctant to give up the good bits we've managed to work out. The fact that she can settle herself through the night and she happily goes down for naps makes me think that she does 'get it', I'm just at a loss as to why bedtime is so hard. Should we try something different for bedtime? I don't want to confuse her, but I don't know how many nights to keep doing this for.

Any help is appreciated...