Happy starter that doesn't work

Hello everyone. My starter is 2.5 months old but I still don't understand how it works. I typically feed it with a strong flour (Allison Very strong white 14 g protein) and it almost triple within 4 hours at 28°C. However, when I use it in a recipe it doesn't seem to work very well. Typically I use 20% of starter and 75-80% of water. To check if the dough rises after kneading it ( I've got a spiral mixer) I cut a small ball out of it and I put it in a long cylindrical glass to check if the volume changes. Nothing typically occurs after few hours at 28°C. I don't know what to do. Do you have any tips?

P.s. I've tried to autolyse, use warm or cold water but nothing.