My DD is 7months and I’ve got the same problem (recently did a thread too). Wouldn’t mind, but she is clearly still tired, and then nights are being impacted. It’s also hard to fit in naps, milk, meals, and anything.
We usually do 2-3hr wake windows, and 3 naps per day, sometimes 4 and a later bedtime. Which never seems enough sleep. I’ve tried pram, cot, dark, light, car etc...
What I am currently doing and it worked (yesterday) not really as well today, is leaving her when she wakes to see if she will resettle. She does self settle at the start of the nap / bedtimes. I will go in and replace the dummy, but no interaction, then increasing the time between me going in and she has been falling back to sleep (about 15-20 minutes later). The other thing I am trying is as I know she will wake up at 30 minutes, going in 5-10minutes before she wakes, and turning on the dream sheep again, or gently nudging her, so she doesn’t wake, but this then resets the sleep cycle. I don’t know if this will work (or yesterday was just fluke), but am willing to try break the habit.
It’s because their sleep cycle is only 30-40minutes long, so they wake after the cycle, and can’t settle / transition into the next.