Morning Levain build suddenly not growing...

Hi all,

First post here! So i have been making loaves for a while with varied success. I recently moved from using a large amount of starter as per James Morton's recipe with a feed the night before, to making a levain build in the morning with a smaller amount of starter and a mix of WW and bread flour. I

I have been using the perfecloaf beginners recipe and making small changes each bake to try and understand the bake better. Recently my last two levain mixes which are 18.5 bread flour, 18.5g WW, 18.5 starter and 37 water for a 500g loaf have been bubbling a little but hardly growing at all, and starting to drop before doubling. My flat is about 24C at the moment, and I usually keep my starter in the fridge for about a week max. with a feed each week. have recently been keeping 50g starter with 1:1 feedings of unbleached all purpose and water.

My last one i tried i took out 2 nights before, and did 2 days of 2x feeds per day and it looked really active, but when I do the levain mix in the morning it seems to loose all activity?? Any ideas? Do i need to spend a few more days upping my regular feeding?