Stiff leg & clench fist/ grabbing things very tightly when lying on her back

Hi mummies or parents, quite a few times when my daughter is laying on her back she keeps her legs stiff as a board and she would clench her fist/ hold onto smth to tightly. Everything I'm reading says hypertonia, her pediatrician keeps saying she's fine, but it seems of to me.. we brought her to physio/ TCM and even neuro when she was like 4-months old, and now that she's 10-month she still has these actions. I would say she's hitting her milestones, like able to crawl, stand on her own and cruise along furnitures, roll back n forth sit unassisted etc. babbles and all too. Anybody faces this issue before? And able to share your exp and solutions with me?