Hi Honey,
I will tell you what I think. E is tired and not so hungry at 6:30pm and that’s why you have a problem with feeding. No let down as no real hunger. She wants to suck the boob (F also wanted) but not as she is very hungry. Count that your boobs are drained a bit after 5pm feed and probably they need a strong signal to have a result.
I had that with F when he was 5-6mo and we were still cluster feeding. He was eating at 3pm, 5pm and at 7:10/7:15pm and at BT feed I was sometimes waiting 20-30min for let down with a screaming baby at my boob! Story was short: I was giving him boob to eat, he didn’t mind to suck for a bit but his suck was too weak so no milk was coming. So he resigned from boob after 2-3min not very hungry, but tired and wanted to sleep. I was offering it once again and once again as thought he had to be hungry. He was starting to scream “noooo, I don’t want”, he got winded up by screaming, so he needed boob to calm down. He was starting to suck, and I though that’s the sign that he is hungry… and the vicious cycle started all over.
When we went to bottle it became very clear to me as there was no problem with “let down” and he was eating very little amounts.
I would try to stop offering so many small feeds (you have 6 per day, aren't you?). So you could go for the routine:
7 milk
10 milk
12:00 lunch
2/3 milk
around 4pm small tea
6:30 milk
I was doing this routine for a long time (two meals w/o breakfast). You have 4 milk feeds in this plan, nicely spaced vs each other, and followed by solid meals. When E will be older you can add solid breakfast.
